This repo contains around 700 (600 Leetcode.com and 100 Algoexpert.io) problems in total, with solutions using Swift and Python

This repo contains my solutions to algorithmic problems in leetcode.com and algoexpert.io written in Swift and Python.
Here is my leetcode profile
And my Algoexpert.io certificate of completion

Show your support by giving it a STAR

About • Topics • Tips • LeetCode.com • AlgoExpert.io • References

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About

I have solved quite a number of problems from several topics. See the below table for further details.

Topics

• Binary Search
• Binary Search Tree
• Binary Tree(Segment Tree)
• N-aray Tree(Trie, Binary Indexed Tree)
• Graph(Dijkstra, Union Find, Kruskal, Prim's, Minimum Spanning Tree, Topological Ordering...etc)
• Stack
• Queue
• Array
• Sorting
• Hash Table
• Heap
• Linked list
• Bit Operation
• Dynamic programming
• Backtracking(Permutations & Combinations & Subsets...etc)
• Math
• and more...

Questions from

• Leetcode
• Algoexpert.io
• Glassdoor
• Interviews
• ...

My other related repos

• Coding Interview Patterns
• Coding Interview Gym
• iOS Interview Gym
• Behavioural Interview Gym
• System Design Interview Gym
• Object Oriented Design Interview Gym

My leetcode account

• ParthoBiswas007

Tips

• Check this Golden post first.
• Whenever you solve a new question with some new techniques/algorithms, try to solve atleast 2 similar problem in a row. This way, your understanding to the new techniques/algorithms will be better.
• Solve all leetcode cards
• ...

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LeetCode

1. Arrays , HashMap, Set

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	1. Two Sum	Python, Swift	---	---	✅ 📌 ⭐ 😭 🧐 😎
02	485. Max Consecutive Ones	Swift
03	476. Number Complement	Swift
04	461. Hamming Distance	Swift
05	9. Palindrome Number	Python
06	88. Merge Sorted Array	Python
07	811. Subdomain Visit Count	Python
08	771. Jewels and Stones	Python
09	414. Third Maximum Number	Python
10	259. 3Sum Smaller	Python
11	16. 3Sum Closest	Python
12	15. 3Sum	Python
13	118. Pascal's Triangle	Python
14	119. Pascal's Triangle II	Python
15	238. Product of Array Except Self	Python, Swift
16	724. Find Pivot Index	Python
17	747. Largest Number At Least Twice of Others	Python
18	581. Shortest Unsorted Continuous Subarray	Python
19	904. Fruit Into Baskets	Python	Article, Video 1, Video 2	Medium	Sliding Window, Two Pointer
20	56. Merge Intervals	Python	Article, Swift
21	334. Increasing Triplet Subsequence	Python	---	Medium	---
22	792. Number of Matching Subsequences	Python	Official	Medium	Very tricky. Check again
23	912. Sort an Array (Merge Sort)	Python	---	Medium	---
24	1118. Number of Days in a Month	Python	---	Easy	---
25	349. Intersection of Two Arrays	Python	Art 1, Art 2	Easy	Very tricky and versatile
26	350. Intersection of Two Arrays II	Python	, ,	Easy	Very tricky and versatile
27	303. Range Sum Query - Immutable	Python	Vid 1	Easy	---
28	560. Subarray Sum Equals K	Python, Swift	Art 1, Art 2, Art 3, Art 4, Art 5, Art 6	Medium	Very tricky and persuasive with Sliding Window but it's not. This is a classic running sum problem
29	325. Maximum Size Subarray Sum Equals k	Python	Art 1	Medium	Very tricky and persuasive with Sliding Window but it's not. This is a classic running sum problem
30	1074. Number of Submatrices That Sum to Target	Python	Art 1, Art 2, Art 3, Art 4	Extremely Hard	Very tricky and hard, check again. Also DP
31	167. Two Sum II - Input array is sorted	Python	---	Easy	Two pointer basics
32	1099. Two Sum Less Than K	Python	---	Easy	Two pointer basics
33	26. Remove Duplicates from Sorted Array	Python	---	Easy	Two pointer basics
34	977. Squares of a Sorted Array	Python	---	Easy	Two pointer basics
35	713. Subarray Product Less Than K	Python	---	Medium	Two pointer ad Sliding Window
36	75. Sort Colors	Python	Vid 1	Medium	Two pointer
37	18. 4Sum	Python	---	Medium	Two pointer
38	11. Container With Most Water	Python	---	Medium	Two pointer
39	202. Happy Number	Python	Art 1	Easy	Fast pointer Slow pointer
40	457. Circular Array Loop	Python	---	Medium	Fast pointer Slow pointer. Check again
41	448. Find All Numbers Disappeared in an Array	Python	---	Easy	Cyclic Sort
42	287. Find the Duplicate Number	Python	---	Medium	Cyclic Sort. TODO: Check all other approaches
43	442. Find All Duplicates in an Array	Python	---	Medium	Cyclic Sort TODO: Check all other approaches
44	41. First Missing Positive	Python	---	Hard	Cyclic Sort, Very important
45	939. Minimum Area Rectangle	Python	Art 1	Medium	Hash and Set, Very important
46	359. Logger Rate Limiter	Python	---	Easy	Hash and Set, Very important
47	48. Rotate Image	Python	Must, Vid 1	Medium	Very important
48	362. Design Hit Counter	Python, Swift	---	Medium	---
49	289. Game of Life	Python, Swift	---	Medium	---
50	54. Spiral Matrix	Python, Swift	Official, Algoexpert.io	Medium	---
51	380. Insert Delete GetRandom O(1)	Python, Swift	Official	Medium	---
52	835. Image Overlap	Python, Swift	Art 1, Art 2	Medium	---
53	1051. Height Checker	Python, Swift	---	Easy
55	683. K Empty Slots	Python, Swift	Art 1, Art 2, Art 3	Hard	TODO: Check monotonic queue approach. Solved it with sliding widow
56	849. Maximize Distance to Closest Person	Python, Swift	Art 1	Easy	Not so easy and intuitive. Can be solve is a variety of way. I have used Binary search(A bit over engineered solution). Can be simplifies
57	283. Move Zeroes	Python, Swift	---	Easy	Not so easy and intuitive. Uses fast and slow pointer
58	163. Missing Ranges	Python, Swift	---	Medium	Man, it's a very trick problem
59	1089. Duplicate Zeros	Python, Swift	Art 1	Easy	Not so easy and intuitive. Check again
60	941. Valid Mountain Array	Python, Swift		Easy
61	731. My Calendar II	Python, Swift		Medium	Merge interval
62	59. Spiral Matrix II	Python, Swift		Medium	loved it
63	525. Contiguous Array	Python, Swift	Art 1	Medium	loved it. Check again
64	379. Design Phone Directory	Python, Swift		Medium
65	280. Wiggle Sort	Python, Swift		Medium
66	246. Strobogrammatic Number	Python, Swift		Easy
67	845. Longest Mountain in Array	Python, Swift		Medium
68	66. Plus One	Python, Swift		Easy
69	957. Prison Cells After N Days	Python, Swift	Art 1, Art 2, Art 3, Art 4, Art 5	Medium
70	1232. Check If It Is a Straight Line	Python, Swift		Easy
71	348. Design Tic-Tac-Toe	Python, Swift	Vid 1, Art 1	Medium	A fucking tricky question
72	1152. Analyze User Website Visit Pattern	Python, Swift	Art 1, Art 2, Art 3, Art 4	Medium	A fucking unclear question and problem. I Fucking disliked it.
73	953. Verifying an Alien Dictionary	Python, Swift		Easy(REALLY!!!)	Don't be fooled by the difficulty label
74	463. Island Perimeter	Python, Swift		Easy	It's very deceiving, to think it as a grapy ad DFS problem, but it's not. Think simply
75	166. Fraction to Recurring Decimal	Python, Swift	Art 1	Medium	Hate this problem. Why do companies ask this shit!!!
75	311. Sparse Matrix Multiplication	Python, Swift	Art 1, Art 2, Art 3, Art 4	Medium	Very tricky
76	896. Monotonic Array	Python, Swift	---	Eassy
77	670. Maximum Swap	Python, Swift	Art 1	Medium
78	825. Friends Of Appropriate Ages	Python, Swift	Art 1	Medium	Think differently from a different angle. Loved this problem
79	189. Rotate Array	Python, Swift	---	Easy	Getting to inplace (O(n) time and O(1) space) solution is tricky.
80	1004. Max Consecutive Ones III	Python, Swift	---	Medium	Solution is tricky.
81	498. Diagonal Traverse	Python, Swift	---	Medium	---
82	766. Toeplitz Matrix	Python, Swift	---	Easy	---
83	1031. Maximum Sum of Two Non-Overlapping Subarrays	Python, Swift	---	Medium	PrefixSum
84	1438. Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit	Python, Swift	(Art 1)[https://tinyurl.com/y69hjhjp], (Art 2)[https://tinyurl.com/y3h2fj2m]	Medium	Sliding window
85	1428. Leftmost Column with at Least a One	Python, Swift	---	Medium	Binary Search
86	914. X of a Kind in a Deck of Cards	Python, Swift	---	Easy (Not So)
87	1275. Find Winner on a Tic Tac Toe Game	Python, Swift	Art 1	Easy (Not So)
88	532. K-diff Pairs in an Array	Python, Swift	Art 1	Medium
89	128. Longest Consecutive Sequence	Python, Swift	Art 1	Hard
90	1423. Maximum Points You Can Obtain from Cards	Python, Swift	Art 1, Art 2	Medium	Very important. Learned new ways of sliding window
91	900. RLE Iterator	Python, Swift	---	Medium	-

2. String

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	3. Longest Substring Without Repeating Characters
02	412. Fizz Buzz	Swift
03	937. Reorder Log Files	Python
03	929. Unique Email Addresses	Python
04	7. Reverse Integer	Python
05	13. Roman to Integer	Python
06	125. Valid Palindrome	Python, Swift
07	161. One Edit Distance	Python
08	1119. Remove Vowels from a String	Python
09	344. Reverse String	Python
10	482. License Key Formatting	Python
11	3. Longest Substring Without Repeating Characters	Python	Vid 1, Vid 2	Medium	📌 Sliding window, Two pointer
12	340. Longest Substring with At Most K Distinct Characters	Python, Swift	Vid 1, Art 1, Art 2	Hard	📌 Sliding window, Two pointer
13	159. Longest Substring with At Most Two Distinct Characters	Python	Vid 1	Hard	📌 Sliding window, Two pointer
14	424. Longest Repeating Character Replacement	Python	Vid 1, Vid 2, Art 1, Art 2, Art 3, Art 4	Medium	📌 Sliding window, Very important
15	76. Minimum Window Substring	Python	Vid 1, Vid 2, Vid 3	Hard	📌 Sliding window, Very important
16	727. Minimum Window Subsequence	Python	Vid 1, Art 1, Art 2	Hard	📌 Sliding window and DP, check the DP approach
17	438. Find All Anagrams in a String	Python, Swift	Must, Art 1	Medium	📌 Sliding window
18	567. Permutation in String	Python	Must	Medium	📌 Sliding window
19	844. Backspace String Compare	Python	---	Easy	📌 Two Pointer
20	809. Expressive Words	Python	Art 1	Medium	📌 Logic ad analytical prolem
21	271. Encode and Decode Strings	Python	Art 1	Medium	📌 TODO: Check the second approach. Very Important
22	299. Bulls and Cows	Python	---	Easy	---
23	833. Find And Replace in String	Python	Art 1	Medium	---
24	49. Group Anagrams	Python	Art 1, Algoexpert.io	Medium	---
25	551. Student Attendance Record I	Python		Easy	---
26	242. Valid Anagram	Python, Swift		Easy	---
27	1358. Number of Substrings Containing All Three Characters	Python, Swift	Art 1	Medium	Sliding Window
28	459. Repeated Substring Pattern	Python, Swift	Art 1	Easy	I fucking love this problem
29	681. Next Closest Time	Python, Swift	Art 1	Medium	I feel stupid after trying my first solution
30	925. Long Pressed Name	Python, Swift	---	Easy
31	949. Largest Time for Given Digits	Python, Swift	---	Easy	Not so easy
32	788. Rotated Digits	Python, Swift	---	Easy	---
33	388. Longest Absolute File Path	Python, Swift	---	Medium	---
34	616. Add Bold Tag in String	Python, Swift	---	Medium	Merge intervals(hidden)
35	678. Valid Parenthesis String	Python, Swift	Art 1, Art 2, Art 3, Art 4	Medium	Super tricky. Much check again
36	273. Integer to English Words	Python, Swift		Hard	MUST check again
37	763. Partition Labels	Python, Swift		Medium
38	819. Most Common Word	Python, Swift	Art 1	Easy
39	350. Intersection of Two Arrays II	Python, Swift	---	Easy	Check the follow-ups
40	249. Group Shifted Strings	Python, Swift	Art 1	Medium	Tricky one
41	158. Read N Characters Given Read4 II - Call multiple times	Python, Swift	Art 1	Hard	Good one
42	415. Add Strings	Python, Swift	Art 1	Easy	---
43	65. Valid Number	Python, Swift	Art 1	HARD	A fucking difficult but important problem. Chack DFA approach
44	791. Custom Sort String	Python, Swift	---	Medium	Loved this problem
45	157. Read N Characters Given Read4	Python, Swift	---	Easy (Not So!)	Loved this problem
46	722. Remove Comments	Python, Swift	Art 1	Medium
47	443. String Compression	Python, Swift	Art 1	Medium

3. Linked List

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	2. Add Two Numbers	Python, Swift	---	Medium	Fundamental
02	707. Design Linked List	Python
03	21. Merge Two Sorted Lists	Python	Algoexpert.io, Vid 1	Easy	Fundamental and very very important
04	234. Palindrome Linked List	Python	---	Easy	Fast pointer Slow pointer
05	24. Swap Nodes in Pairs	Python
06	141. Linked List Cycle	Python	---	Easy	Fast pointer Slow pointer
07	142. Linked List Cycle II	Python	Art 1, Art 2, AlgoExpert.io	Medium	Fast pointer Slow pointer
08	876. Middle of the Linked List	Python	---	Easy	Fast pointer Slow pointer
09	143. Reorder List	Python	---	Medium	Fast pointer Slow pointer
10	19. Remove Nth Node From End of List	Python	---	Medium	Fast pointer Slow pointer
11	817. Linked List Components	Python	Art 1	Medium	Uses set/dictionary
12	206. Reverse Linked List	Python	Vid 1, Vid 2	Easy	Fundamental
13	92. Reverse Linked List II	Python	educative.io, Art 2	Medium	Fundamental and very important
14	25. Reverse Nodes in k-Group	Python	educative.io, Art 1, Art 2	Hard	Fundamental. TODO: Check again
15	24. Swap Nodes in Pairs	Python	educative.io	Medium	Fundamental
16	61. Rotate List	Python	educative.io	Medium	Fundamental
17	328. Odd Even Linked List	Python	Art 1	Medium	Fundamental
18	148. Sort List	Python	Vid 1, Vid 2, Vid 3, Art 1	Medium	Fundamental
19	23. Merge k Sorted Lists	Python	educative.io, Art 1	Hard	Very important. TODO: Check heap approach
20	160. Intersection of Two Linked Lists	Python	Art 1, Art 2	Easy	---
21	138. Copy List with Random Pointer	Python	Vid 1, Art 1	Medium	TODO: Check again. Very important. Learned a lot of things
22	430. Flatten a Multilevel Doubly Linked List	Python	backtobackswe.com, Vid 1, Art 1	Medium	TODO: Check again. Very important. Learned a lot of things
23	146. LRU Cache	Python	Vid 1, backtobackswe.com, algoexpert.io	Hard	TODO: Check again. Very important. Learned a lot of things
24	460. LFU Cache	Python	Vid 1, backtobackswe.com, algoexpert.io	Hard	TODO: Check again. Very important. Learned a lot of things
25	460. LFU Cache	Python	Art 1	Easy
26	708. Insert into a Sorted Circular Linked List	Python, Swift	Art 1	Medium
27	203. Remove Linked List Elements	Python, Swift	---	Easy
28	432. All O`one Data Structure	Python, Swift	Art 1	Hard	Super hard and super important
29	426. Convert Binary Search Tree to Sorted Doubly Linked List	Python, Swift	Art 1	Medium	Super important
30	1265. Print Immutable Linked List in Reverse	Python, Swift	Art 1	Medium	Really?? Are we supposed to solve a puzzle in an interview?

4. Stack, Queue

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	20. Valid Parentheses	Python
02	155. Min Stack	Python
03	84. Largest Rectangle in Histogram	Python	Video 01, Video 02, Article 01, Article 02	Hard	📌 Need to revise
04	394. Decode String	Python	---	Medium	📌 Classic stack problem
05	239. Sliding Window Maximum	Python	Video 1, Official, Art 1, Art 2, Art 3, Art 4	Hard	📌 Can be solved using Heap, Deque and DP
06	739. Daily Temperatures	Python	Video 1, Video 2, Art 1	Medium	📌 TODO: Check again. A tricky one
07	150. Evaluate Reverse Polish Notation	Python, Swift	Vid 1	Medium	---
08	341. Flatten Nested List Iterator	Python, Swift	Vid 1, Art 1, Art 2, Art 3, Art 4, Art 5	Medium	TODO: Check again. Very Important. Learned new things
09	173. Binary Search Tree Iterator	Python, Swift, Swift	Vid 1, Art 1	Medium	TODO: Check again. Very Important. Learned new things
10	284. Peeking Iterator	Python, Swift	Art 1	Medium	---
11	281. Zigzag Iterator	Python, Swift	Art 1	Medium	---
12	946. Validate Stack Sequences	Python, Swift	Art 1, Art 2	Medium	---
13	862. Shortest Subarray with Sum at Least K	Python, Swift	Art 1, Art 2, Art 3, Art 4	Hard	Learned Monotonic Queue. Very interesting problem
14	346. Moving Average from Data Stream	Python, Swift		Easy
15	71. Simplify Path	Python, Swift		Medium
16	1249. Minimum Remove to Make Valid Parentheses	Python, Swift	Official	Medium	Must check
17	636. Exclusive Time of Functions	Python, Swift	Art 1	Medium	Must check
18	921. Minimum Add to Make Parentheses Valid	Python, Swift	---	Medium	---
19	1209. Remove All Adjacent Duplicates in String II	Python, Swift	---	Medium	---
20	227. Basic Calculator II	Python, Swift	Art 1	Medium	---

5. Heaps

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	358. Rearrange String k Distance Apart	Python	Educative.io, Educative.io 2	Hard	📌 Similar to 621. Task Scheduler. Very Important. TODO: Check Heap approach
02	347. Top K Frequent Elements	Python	educative.io, Helper 1, Helper 2, heapq, Counter	Medium	---
03	767. Reorganize String	Python	---	Medium	Also check Greedy approach
04	621. Task Scheduler	Python, Swift	Ex 1, Ex 2, Vid 1, Vid 2, Vid 3, Vid 4	Medium	📌 Extremely tricky. Classic problem
05	295. Find Median from Data Stream	Python	algoexpert.io, educative.io, educative.io 2, codinginterviewclass.com, Official, FollowUp 1	Hard	📌 Very Tricky and important. TODO: Check again
06	480. Sliding Window Median	Python	educative.io, Vid 1	Hard	📌 Sliding window with 2 heap. very important
07	4. Median of Two Sorted Arrays	Python	Article 01, Art 2 Video 1	Hard	📌 Classic problem
08	215. Kth Largest Element in an Array	Python	Art 01, Algoexpert.io, educative.io	Medium	📌 Also check Quickselect method.
09	373. Find K Pairs with Smallest Sums	Python	educative.io	Hard	📌 TODO: Check again.
10	973. K Closest Points to Origin	Python	Algoexpert.io, educative.io, Vid 1	Medium	📌 Also check Quickselect and heap method
11	451. Sort Characters By Frequency	Python	Algoexpert.io, educative.io	Medium	📌 Also check Quickselect and heap method
12	692. Top K Frequent Words	Python	Algoexpert.io, educative.io	Medium	📌 Also check Quickselect and heap method
13	703. Kth Largest Element in a Stream	Python	educative.io	Medium	📌 ---
14	895. Maximum Frequency Stack	Python	educative.io, Art 1	Hard	📌 TODO: Check again
15	378. Kth Smallest Element in a Sorted Matrix	Python	educative.io	Hard	📌 TODO: Check again the Binary Search approach. Very important
16	632. Smallest Range Covering Elements from K Lists	Python	educative.io	Hard	📌 TODO: Check again. Very important
17	846. Hand of Straights	Python	Art 1	Medium	📌 TODO: Check again. Very important
18	1167. Minimum Cost to Connect Sticks	Python	Art 1	Medium
19	1102. Path With Maximum Minimum Value	Python	Art 1, Art 2, Art 3	Medium	Dijekstra

6. Binary Search

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	704. Binary Search	Python	---	Easy	Basics
03	240. Search a 2D Matrix II	Python	Video 01, Video 02
04	74. Search a 2D Matrix	Python	Video 01, Video 02
05	1011. Capacity To Ship Packages Within D Days	Python	Discussion 1, Discussion 2, Discussion 3	Medium	Difficult to spot the pattern, revise again
06	410. Split Array Largest Sum	Python	Vid 1, Art 1, Art 2	Hard	📌 TODO: Check again. It's a fucking difficult and interesting and important
07	4. Median of Two Sorted Arrays	Python	Article 01, Art 2 Video 1	Hard	📌 Classic problem
08	981. Time Based Key-Value Store	Python	Article 01	Medium	📌
09	**222. Count Complete Tree Nodes**	Python, Swift	Theory, Official Solution, Fantastic idea!	Medium	📌 BS within BS
10	1231. Divide Chocolate	Python	Art 1, Art 2, Art 3, Vid 1	Hard	📌 Not done. Check again. Solve all similar question
11	69. Sqrt(x)	Python	---	Easy	📌 Binary Search Template I
12	374. Guess Number Higher or Lower	Python	---	Easy	📌 Binary Search Template I
13	33. Search in Rotated Sorted Array	Python, Swift	Educative.io	Medium	📌 Binary Search Template I, Very important
14	81. Search in Rotated Sorted Array II	Python	---	Medium	📌 Binary Search Template I, very important
15	278. First Bad Version	Python	---	Easy	📌 Binary Search Template II
16	162. Find Peak Element	Python	---	Medium	📌 Binary Search Template II
17	153. Find Minimum in Rotated Sorted Array	Python, Swift	---	Medium	📌 Binary Search Template II
18	154. Find Minimum in Rotated Sorted Array II	Python	---	Hard	📌 Binary Search Template II, not done
19	34. Find First and Last Position of Element in Sorted Array	Python, Swift	Vid 1, Educative.io	Medium	📌 Binary Search Template III
20	658. Find K Closest Elements	Python	Vid 1, educative.io	Medium	📌 Binary Search Template III. TODO: Check Heap approach which is not done
21	702. Search in a Sorted Array of Unknown Size	Python	Educative.io	Medium	📌 Binary Search Template I
22	378. Kth Smallest Element in a Sorted Matrix	Python	educative.io	Hard	📌 TODO: Check again the Binary Search approach. Very important
23	1146. Snapshot Array	Python	Art 1	Medium	Tricky use of binary search
24	1170. Compare Strings by Frequency of the Smallest Character	Python	---	Easy	Binary Search, Very important
25	852. Peak Index in a Mountain Array	Python, Swift	---	Easy	---
25	209. Minimum Size Subarray Sum	Python, Swift	---	Medium	Sliding window and Binary Search
26	363. Max Sum of Rectangle No Larger Than K	Python, Swift	Vid 1, Vid 2, Art 1, Art 2, Art 3	Hard	DP and BS. Disn't understand S part. TODO: Check again
27	875. Koko Eating Bananas	Python, Swift	---	Medium	I loved this problem
28	1060. Missing Element in Sorted Array	Python, Swift	---	Medium	I loved this problem
29	1292. Maximum Side Length of a Square with Sum Less than or Equal to Threshold	Python, Swift	Art 1	Medium	I loved this problem. Sliding window and Binary Search
30	774. Minimize Max Distance to Gas Station	Python, Swift	Vid 1, Art 1, Art 2, Art 1	Hard	I loved this problem. Very important
31	1231. Divide Chocolate	Python, Swift	Art 1, Art 2, Art 3	Hard	I loved this problem. Very important
32	1268. Search Suggestions System	Python, Swift	Art 1, Art 2, Art 3	Medium	I loved this problem. Very versatile, ca be solved in a lot of different ways
33	540. Single Element in a Sorted Array	Python, Swift		Medium	---
34	441. Arranging Coins	Python, Swift		Easy	---
35	154. Find Minimum in Rotated Sorted Array II	Python, Swift	Art 1	Medium	VERY IMPORTANT

7. Binary Tree

Binary Tree Bootcamp

Leetcode problems with solutions and tutorials/videos

Check this [golden](https://tinyurl.com/ujopecz) post.

#	Title	Solution	Tutorial	Level	Remarks
01	226. Invert Binary Tree	Python
02	101. Symmetric Tree	Python
03	102. Binary Tree Level Order Traversal	Python
04	107. Binary Tree Level Order Traversal II	Python
05	103. Binary Tree Zigzag Level Order Traversal	Python
06	104. Maximum Depth of Binary Tree	Python	Explanation
07	100. Same Tree	Python
08	111. Minimum Depth of Binary Tree	Python		Easy	---
09	110. Balanced Binary Tree	Python	Video 1, Article 1, Article 2	Easy	---
10	105. Construct Binary Tree from Preorder and Inorder Traversal	Python	Art 1, Art 2, Vid 1	Medium	DFS, Very Important
11	106. Construct Binary Tree from Inorder and Postorder Traversal	Python, Swift	Art 1	Medium	DFS, Very Important
12	889. Construct Binary Tree from Preorder and Postorder Traversal	Python	Vid 1, Art 1, Art 2	Medium	📌 TODO: Check again. Important
13	124. Binary Tree Maximum Path Sum	Python, Swift	Art 1, Art 2, Vid 1, AlgoExpert	Very Hard	Very important and tricky
14	979. Distribute Coins in Binary Tree	Python	Art 1, Art 2, Art 3	Medium	Very important. Postorder DFS
15	116. Populating Next Right Pointers in Each Node	Python	Art 1, Art 2, Art 3	Medium	BFS/DFS, Level order traversal
16	117. Populating Next Right Pointers in Each Node II	Python	Vid 1, Vid 2	Medium	Very tricky, check again
17	199. Binary Tree Right Side View	Python, Swift	---	Medium	---
18	863. All Nodes Distance K in Binary Tree	Python	Vid 1, Art 1, Art 2	Medium	A combination of graph and tree. TODO: Check again. Very important
19	301. Remove Invalid Parentheses	Python	Vid 1, Vid 2, Art 1	Hard	TODO: Not done, Check again. Very important. BFS and DFS
20	112. Path Sum	Python	Art 1	Easy	---
21	113. Path Sum II	Python	Art 1, Art 2	Medium	---
22	437. Path Sum III	Python	Educative.io, Art 1, Art 2	Medium	📌 A good example of Prefix Sum and DFS. Very Important
23	543. Diameter of Binary Tree	Python, Swift	Educative.io, Art 1	Medium	📌 Important
24	1110. Delete Nodes And Return Forest	Python	Vid 1, Vid 2, Art 1, Art 2	Medium	📌 **TODO: Check again. Important
25	257. Binary Tree Paths	Python	---	Easy	DFS
26	1145. Binary Tree Coloring Game	Python	Art 1, Art 2	Medium	DFS
27	298. Binary Tree Longest Consecutive Sequence	Python	Art 1	Medium	DFS
28	951. Flip Equivalent Binary Trees	Python	Vid 1, Art 1	Medium	DFS
29	528. Random Pick with Weight	Python	Vid 1, Art 1	Medium	Very tricky
30	236. Lowest Common Ancestor of a Binary Tree	Python, Swift	Vid 1, Vid 2, Algoexpert.io, Official, Art 1, Art 2, Art 3	Medium	TODO: Check Again. Very Important
31	114. Flatten Binary Tree to Linked List	Python	Art 1	Medium	Classic Prolem
32	297. Serialize and Deserialize Binary Tree	Python, Swift	Vid 1	Hard	Classic Prolem
33	993. Cousins in Binary Tree	Python, Swift		Easy(Not so)
34	572. Subtree of Another Tree	Python, Swift	Art 1	Easy(Not so)
35	314. Binary Tree Vertical Order Traversal	Python, Swift	Vid 1	Medium
36	987. Vertical Order Traversal of a Binary Tree	Python, Swift	Vid 1, Art 1, Art 2	Medium
37	958. Check Completeness of a Binary Tree	Python, Swift	Art 1	Medium
38	865. Smallest Subtree with all the Deepest Nodes	Python, Swift	Art 1, Art 2, Art 3, Art 4	Medium	Vary ambigious question
39	1315. Sum of Nodes with Even-Valued Grandparent	Python, Swift	--	Medium	--
40	129. Sum Root to Leaf Numbers	Python, Swift	--	Medium	--
41	938. Range Sum of BST	Python, Swift	--	Medium	--
42	1305. All Elements in Two Binary Search Trees	Python, Swift	--	Medium	--
43	536. Construct Binary Tree from String	Python, Swift	--	Medium	--
44	652. Find Duplicate Subtrees	Python, Swift	--	Medium	--

8. Binary Search Tree

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	701. Insert into a Binary Search Tree	Python	---	Medium	Fundamentals
02	700. Search in a Binary Search Tree	Python	---	Easy	Fundamentals
03	270. Closest Binary Search Tree Value	Python	---	Easy	Fundamentals
04	450. Delete Node in a BST	Python	---	Medium	Fundamentals
05	98. Validate Binary Search Tree	Python	---	Medium	Fundamentals
06	94. Binary Tree Inorder Traversal	Python, Swift	---	Medium	Fundamentals
07	144. Binary Tree Preorder Traversal	Python	---	Medium	Fundamentals
08	145. Binary Tree Postorder Traversal	Python	---	Hard	Fundamentals
09	108. Convert Sorted Array to Binary Search Tree	Python	---	Easy	Fundamentals
10	109. Convert Sorted List to Binary Search Tree	Python	---	Medium	Classic problem. Very important
11	729. My Calendar I	Python, Swift	Art 1, Art 2	Medium	Use self balancing BST for O(nlogn) solution. Very important
12	449. Serialize and Deserialize BST	Python, Swift	Art 1	Medium	---
13	1008. Construct Binary Search Tree from Preorder Traversal	Python, Swift	Art 1, Art 2, Art 3, Art 4	Medium	---
14	653. Two Sum IV - Input is a BST	Python, Swift	-	Easy	---
15	99. Recover Binary Search Tree	Python, Swift	-	Hard	Very important, check again
16	230. Kth Smallest Element in a BST	Python, Swift	-	Medium	Easy peasy

9. N-Ary Tree

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	589. N-ary Tree Preorder Traversal	Python
02	590. N-ary Tree Postorder Traversal	Python
03	429. N-ary Tree Level Order Traversal	Python
04	559. Maximum Depth of N-ary Tree	Python
05	431. Encode N-ary Tree to Binary Tree	Python	Explanation
06	428. Serialize and Deserialize N-ary Tree	Python	Art 1, Official	Hard	Very important

10. Tree

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	315. Count of Smaller Numbers After Self	Python	Article 1, Article 2, Vid 1, Vid 2	Hard (Very)	📌 Very hard and important. First learn BIT, ST, AVL-Tree and Red-Black Tree then try again

11. Tries

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	208. Implement Trie (Prefix Tree)	Python
02	211. Add and Search Word. Data structure design	Python	Video 01, Video 02
03	642. Design Search Autocomplete System	Python	Article 01, Video 01	Hard	---
04	472. Concatenated Words	Python	Art 01, Art 02	Hard	Very important
05	588. Design In-Memory File System	Python	---	Hard	---
06	212. Word Search II	Python, Swift	Art 1	Hard	---
07	1233. Remove Sub-Folders from the Filesystem	Python, Swift	Art 1	Medium	Didn't think of it as a trie. Good problem

12. Graphs

BFS, DFS, Dijkstra, Floyd–Warshall, Bellman-Ford, Kruskal, Prim's, Minimum Spanning Tree, Topological Ordering, Union Find.

Follow this golden rule to approach any graph problem.

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	207. Course Schedule	Python	educative.io	Medium	📌 Very Important. Check again. BFS, Topological Sort
02	210. Course Schedule II	Python	educative.io	Medium	📌 Very Important. Check again. BFS, Topological Sort
03	269. Alien Dictionary	Python, Swift	educative.io, Vid 1, Vid 2, Vid 3	Hard	📌 Very Important. Check again. BFS, Topological Sort
04	444. Sequence Reconstruction	Python	educative.io	Medium/Hard	📌 Check again. BFS, Topological Sort
05	310. Minimum Height Trees	Python	educative.io	Hard	📌 TODO: Check again, very hard, didn't get the intuition. BFS, Topological Sort
06	329. Longest Increasing Path in a Matrix	Python	Official, Art 1, Art 2	Hard	** 📌 TODO: Not Done, very hard and important. DP, Topological Sort **
07	1203. Sort Items by Groups Respecting Dependencies	Python		Hard	📌 TODO: Not Done, very hard, didn't get the intuition. BFS, Topological Sort
08	695. Max Area of Island	Python	---	Medium	DFS
09	200. Number of Islands	Python	Algoexpert.io - DFS, Union Find, Art 1	Medium	DFS + DFS, Union Find
10	305. Number of Islands II	Python	Union Find, Art 0, Art 1, Art 2, Art 3, Art 4, Art 5	Hard	Union Find
11	399. Evaluate Division	Python	Art 0, Art 1, Art 2, Art 3, Art 4, Art 5	Medium	TODO: Solve it using Union Find
12	841. Keys and Rooms	Python	codinginterviewclass.com, Art 1, Art 2	Medium	BFS, DFS
13	490. The Maze	Python	codinginterviewclass.com, Vid 1, Art 1, Art 2, Art 3, Art 4, Art 5	Medium	Modified BFS and DFS
14	130. Surrounded Regions	Python	codinginterviewclass.com, Art 1, Art 2	Medium	TODO: Solve it using Union Find. Modified BFS and DFS
15	127. Word Ladder	Python	backtobackswe.com, Official, Art 1	Medium	Very important and tricky. Modified BFS. Shortest Path finding
16	126. Word Ladder II	Python	backtobackswe.com, Official, Vid 1, Vid 2, Art 1 - Must	Hard	TODO: Not Done. Extremely tricky. Modified BFS. Learned Bidirectional Search
17	785. Is Graph Bipartite?	Python, Swift	backtobackswe.com, Official	Medium	Important, Learned new things. Undirected Graph
18	133. Clone Graph	Python, Swift	backtobackswe.com, Official	Medium	Important, Learned new things. Undirected Graph
19	332. Reconstruct Itinerary	Python	Vid 1, Vid 2, Art 1, Art 2, Art 3, Art 4	Medium	Important, Learned new things. Directed Graph. Eulerian path and top Sort
20	1153. String Transforms Into Another String	Python	Vid 1, Vid 2, Art 1, Art 2, Art 3, Art 4, Art 5, Art 6	Extremely Hard	TODO: Check again. Very Important and tricky, Learned new things. Digraph.
21	743. Network Delay Time	Python	Official, Dijkstra 1, Dijkstra 2, Vid 1, Art 1, Art 2, Art 3, Art 4	Medium	TODO: Check again. Very Important. Learned (Dijkstra, Bellman, Floyed). Check references section
22	261. Graph Valid Tree	Python	Art 1, Art 2, Art 3, Art 4	Medium	Important. BFS, DFS and Union Find
23	1168. Optimize Water Distribution in a Village	Python	Art 1, Art 2, Art 3, Art 4	Hard	TODO: Check AGain. Prim's and Kruskal's algorithm. Important.
24	1197. Minimum Knight Moves	Python	Art 1	Medium	TODO: Check AGain. Important.
25	1066. Campus Bikes II	Python	Vid 1, Art 1	Medium	📌 TODO: CHECK Dijkstra approach again. Backtracking solution is getting TLE. Solve it and implement it with DP also. Very important
26	752. Open the Lock	Python	Art 1, Art 2	Medium	📌 TODO: CHECK again. Very important and interesting problem. Loved it
27	489. Robot Room Cleaner	Python, Swift	Vid 1, Vid 2, Art 1	Hard	📌 TODO: CHECK again. Very important and interesting problem. I fucking loved it
28	1136. Parallel Courses	Python, Swift	---	Hard	📌 Topological sort.
29	947. Most Stones Removed with Same Row or Column	Python, Swift	Vid 1, Art 1, Vid 2, Art 2, Art 3	Medium	📌 DFS and Union FInd
30	1042. Flower Planting With No Adjacent	Python, Swift	---	Easy	📌 Could be done using DFS, BFS
31	994_Rotting_Oranges	Python, Swift	---	Medium	📌 BFS
32	909. Snakes and Ladders	Python, Swift	Art 1, Art 2, Art 3, Vid 1, Vid 2,	Medium	📌 BFS. Check again
33	1192. Critical Connections in a Network	Python, Swift	Art 1, Art 2, Art 3, Art 4, Vid 1, Vid 2, Vid 3	Hard	📌 Important, Learned new things.Tarjans SCCs algorithm. Check again
34	694. Number of Distinct Islands	Python, Swift	Art 1, Art 2	Medium	📌
35	997. Find the Town Judge	Python, Swift	---	Easy	📌
36	733. Flood Fill	Python, Swift	---	Easy	📌
37	339. Nested List Weight Sum	Python, Swift	---	Easy	📌
38	1026. Maximum Difference Between Node and Ancestor	Python, Swift	---	Medium	📌
39	721. Accounts Merge	Python, Swift	---	Medium	📌 Loved it and hated it. Learned a lot. Very insightfull and tricky, deceiving problem. Be very carefull with your choice
40	1123. Lowest Common Ancestor of Deepest Leaves	Python, Swift	---	Medium	📌 Loved it and hated it.
41	419. Battleships in a Board	Python, Swift	---	Medium	📌 Union FInd and or DFS.
42	934. Shortest Bridge	Python, Swift	Art 1	Medium	📌 DFS and BFS
43	317. Shortest Distance from All Buildings	Python, Swift	Art 1	Hard	📌 BFS, a must do problem
44	93. Restore IP Addresses	Python, Swift	---	Medium	📌 A must do problem. Backtracking
45	1424. Diagonal Traverse II	Python, Swift	---	Medium	📌 Very interesting one.
46	364_Nested_List_Weight_Sum_II	Python, Swift	---	Medium	📌 Hidden DFS
47	1245. Tree Diameter	Python, Swift	Art 1	Medium	📌 Learned, 2 BFS. Important and interesting
48	1376. Time Needed to Inform All Employees	Python, Swift	Art 1	Medium	📌 BFS, DFS
49	286. Walls and Gates	Python, Swift	---	Medium	📌 BFS, DFS
50	1138. Alphabet Board Path	Python, Swift	---	Medium	📌 BFS
51	690. Employee Importance	Python, Swift	---	Easy	📌 BFS
52	**1631. Path With Minimum Effort **	Python, Swift	---	Medium	📌 BFS, DFS, Binary search
53	**547. Friend Circles **	Python, Swift	Art 1, Art 2	Medium	📌 BFS, DFS, Union Find

13. Recursion, Iteration

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	509. Fibonacci Number	Python
02	50. Pow(x, n)	Python
00	It's a general topics which has been covered on Backtracking and graph problems	---	---	---	---

14. Backtracking

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	211. Add and Search Word. Data structure design	Python	Video 01, Video 02
02	37. Sudoku Solver	Python	Video 01, Video 02
03	52. N-Queens II	Python	Video 01, Video 02
04	784. Letter Case Permutation	Python	---	Easy	Backtracking Fundamentals
05	1219. Path with Maximum Gold	Python	---	Medium	📌 ---
06	79. Word Search	Python	Article 1	Medium	Backtracking Fundamentals
07	679. 24 Game	Python	Art 1, Art 2, Art 3, Official	Very Hard	📌 Very tricky and important. Revise again.
08	1066. Campus Bikes II	Python	Vid 1, Art 1	Medium	📌 TODO: CHECK Dijkstra approach again. Backtracking solution is getting TLE. Solve it and implement it with DP also. Very important
09	1087. Brace Expansion	Python	---	Medium	📌 ---
10	78. Subsets	Python	Video 1, Video 2, Video 3, Article 1, educative.io	Medium	📌 TODO: check bit manipulation
11	90. Subsets II	Python	Video 1, Video 2, Video 3, Article 1, educative.io	Medium	📌
12	46. Permutations	Python	codinginterviewclass.com, algoexpert.io, educative.io, Article 1, Article 2	Medium	Backtracking Fundamentals
13	47. Permutations II	Python	codinginterviewclass.com, algoexpert.io, educative.io, Article 1	Medium	Backtracking Fundamentals
14	31. Next Permutation	Python, Swift	backtobackswe.com, Vid 1, Art 1, Official	Medium	Backtracking
15	77. Combinations	Python	codinginterviewclass.com	Medium	Backtracking
16	39. Combination Sum	Python	Article 1, Article 2	Medium	Backtracking Fundamentals
17	40. Combination Sum II	Python	---	Medium	Backtracking Fundamentals
18	17. Letter Combinations of a Phone Number	Python	Video 1, Video 2 - paid course, Article 1	Medium	Backtracking Fundamentals
19	22. Generate Parentheses	Python, Swift	educative.io, Video 1, Article 1	Medium	Backtracking Fundamentals
20	1088. Confusing Number II	Python, Swift	Art 1, Ref 1	Hard	Very interesting
21	465. Optimal Account Balancing	Python, Swift	Art 1	Hard	Loved the question, awsome real life description
22	1079. Letter Tile Possibilities	Python, Swift	---	Medium	📌 Could be done using DFS, backtracking
23	60. Permutation Sequence	Python, Swift	Art 1	Medium	📌 What an awesome question and smart solution. loved it.

15. Greedy

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	1055. Shortest Way to Form String	Python	Art 1, Art 2, Art 3, Art 4, Art 5	Medium	📌 Very important and hard problem
02	1057. Campus Bikes	Python	Video 01, Article 01	Medium	📌 Solve 1066. Campus Bikes II using DP, DFS and Priority Queue
03	1007. Minimum Domino Rotations For Equal Row	Python	Vid 1, Vid 2,Art 1,Art 2,Art 3	Medium	📌 Hard to spot if it is a Greedy. Very Important
04	406. Queue Reconstruction by Height	Python	Article 1, Article 2	Medium	📌 Fundamentals
05	621. Task Scheduler	Python	Ex 1, Ex 2, Vid 1, Vid 2, Vid 3, Vid 4	Medium	📌 Extremely tricky. Classic problem
06	392. Is Subsequence	Python	Ex 1, Ex 3	Easy	📌
07	55. Jump Game	Python	Official , Art 1	Medium	📌 Must Check. Learned a lot
08	45. Jump Game II	Python	educative.io, Vid 1, Vid 2, Vid 3, Art 1	Hard	📌
09	767. Reorganize String	Python	---	Medium	Also check Heap approach
10	435. Non-overlapping Intervals	Python	Vid 1, Art 1	Medium	Classic problem
11	57. Insert Interval	Python	Must	Hard	Greedy and Merge interval
12	986. Interval List Intersections	Python, Swift	---	Medium	Greedy and Two Pointer
13	252. Meeting Rooms	Python	Official	Easy	Greedy and uses heap
14	253. Meeting Rooms II	Python, Swift	Official	Medium	Greedy and uses heap
15	759. Employee Free Time	Python	Educative.io	Hard	Greedy and uses heap. Not done. Check again
16	659. Split Array into Consecutive Subsequences	Python	Art 0, Art 1, Art 2, Art 3, Vid 1, Art 4	Medium	📌 It's a fucking unclear problem. TODO: Not done. Check again later
17	68. Text Justification	Python	Vid 1, Vid 2, Vid 3, Art 0, Art 1	Hard	TODO: Check again later. Very Important
18	134. Gas Station	Python, Python, Swift	Vid 1, Art 1	Medium	TODO: Check again later. Very Important
19	1288. Remove Covered Intervals	Python	Art 1	Medium	Line Swap with Greedy. A must read solution. A gold mie, learned a lot
20	1296. Divide Array in Sets of K Consecutive Numbers	Python, Swift	Art 1	Medium	---
21	984. String Without AAA or BBB	Python, Swift	Art 1	Medium	---

16. Dynamic Programming

Follow this golden rule to approach any DP problem.

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	53. Maximum Subarray	Python	Vid 1, Algoexpert.io	Easy	Kadane's Algorithm
02	518. Coin Change 2	Python	educative.io, Vid 1, codinginterviewclass.com, Algoexpert.io	Medium	Unbounded Knapsack
03	322. Coin Change	Python	educative.io, Vid 1, Algoexpert.io	Medium	Unbounded Knapsack
04	72. Edit Distance	Python	educative.com, algoexpert.io, codinginterviewclass.com, Vid 1, Vid 2	Hard	TODO: Check again. Very important and classic. Levenshtein Distance
05	70. Climbing Stairs	Python	educative.io	Easy	Fibonacci sequence pattern
06	96. Unique Binary Search Trees	Python	educative.io, Vid 1, Art 1, Vid 2, Vis 3	Medium	📌 Fundamentals
07	95. Unique Binary Search Trees II	Python	educative.io	Medium	---
08	221. Maximal Square	Python	Video 01, Video 02
09	85. Maximal Rectangle	Python	Video 01
10	42. Trapping Rain Water	Python	Article 01	Hard	📌 Check stack and 2 pointers based solutions
11	300. Longest Increasing Subsequence	Python	educative.io, codinginterviewclass.com, algoexpert.io, Vid 01, Vid 2	Medium	📌 Need to check Binary Search approach, which is a lot harder
12	1143. Longest Common Subsequence	Python	educative.io, algoexpert.io	Medium	📌 Classic DP
13	5. Longest Palindromic Substring	Python	educative.io, algoexpert.io, Vid 1	Medium	📌 Classic DP
14	1066. Campus Bikes II	Python		Medium	📌 TODO: Backtracking solution is getting TLE. Solve it and implement it with DP also
15	121. Best Time to Buy and Sell Stock	Python	Vid 1	Easy	Fundamental
16	122. Best Time to Buy and Sell Stock II	Python	Video 01	Easy	More like Greedy
17	123. Best Time to Buy and Sell Stock III	Python	Vid 1, Vid 2	Hard	Fundamental
18	188. Best Time to Buy and Sell Stock IV	Python	Vid 1, Vid 2	Hard	Getting "Memory Limit Exceeded"
19	309. Best Time to Buy and Sell Stock with Cooldown	Python	Must, Art0, Art1, Must 2 , Art 2, Art 3	Medium	Very tricky, must check again. Couldn't solve
20	714. Best Time to Buy and Sell Stock with Transaction Fee	Python	Must Read , Art 2	Medium	More like Greedy, but DP
21	198. House Robber	Python	Must, educative.io	Easy	A Gold Mine
22	213. House Robber II	Python	Art 1, Art 2	Medium	---
23	337. House Robber III	Python	Art 1	Medium	Another gold mine, hidden greedy and DFS
24	416. Partition Equal Subset Sum	Python	educative.io, Art 1, Vid 1, Vid 2, Vid 3, Vid 4	Medium	0/1 Knapsack, Very important
25	494. Target Sum	Python	educative.io, MUST MUST READ	Medium	0/1 Knapsack, Very important. TODO: Not DOne. Check again
26	343. Integer Break	Python	Art 1, Art 2	Medium	Unbounded Knapsack. TODO: Not Done. Check again
27	516. Longest Palindromic Subsequence	Python	educative.io, Vid 1, Vid 2	Medium	---
28	647. Palindromic Substrings	Python	educative.io	Medium	---
29	680. Valid Palindrome II	Python	educative.io, Art 1, Art 2	Medium	---
30	1312. Minimum Insertion Steps to Make a String Palindrome	Python	educative.io	Hard	---
31	132. Palindrome Partitioning II	Python	educative.io, algoexpert.io, Vid 1, Vid 2	Hard	TODO: Check again. Very difficult and important
32	718. Maximum Length of Repeated Subarray	Python	educative.io	Medium	Longest Common Substring variation
33	583. Delete Operation for Two Strings	Python	educative.io	Medium	---
34	1092. Shortest Common Supersequence	Python	educative.io, Art 1	Hard	TODO: Not Done
35	115. Distinct Subsequences	Python	educative.io	Hard	TODO: Check again
36	97. Interleaving String	Python	educative.io, Vid 1	Hard	TODO: Check again. Very difficult and tricky to understand
37	1048. Longest String Chain	Python	Art 1	Medium	Modified LIS
38	801. Minimum Swaps To Make Sequences Increasing	Python	Art 1, Art 2	Medium	TODO: Check again. Very analytical and tricky to come up with
39	279. Perfect Squares	Python	Must, Vid 1, Vis 2	Medium	TODO: Check again. Very Important. Very analytical and tricky to come up with
40	139. Word Break	Python	Must, Vid 1, Vis 2, Vid 3	Medium	TODO: Check again. Very Important.
41	62. Unique Paths	Python, Swift	Vid 1, Art 1, Art 2	Medium	TODO: Check again
42	152. Maximum Product Subarray	Python, Swift	Vid 1, Art 1	Medium	Kadane's algorithm on multiplication
43	64. Minimum Path Sum	Python, Swift	---	Medium	---
44	91. Decode Ways	Python, Swift	Vid 1	Medium	---
45	975. Odd Even Jump	Python, Swift	Vid 1, Art 1	Hard	DP using stack. Vary tricky and Interesting problem, loved it
46	562. Longest Line of Consecutive One in Matrix	Python, Swift	Art 1, Art 2	Medium
47	552. Student Attendance Record II	Python, Swift	Art 1, Art 2, Art 3	Hard	This is a FUCKING difficult DP problem. Don't dare to solve it
48	1320. Minimum Distance to Type a Word Using Two Fingers	Python, Swift	Vid 1, Art 1, Art 2, Art 3, Art 4	Hard	Important. TODO: Check again
49	688. Knight Probability in Chessboard	Python, Swift	Art 1, Art 2, Art 3	Medium(Really!)	Important, and fucking difficult. TODO: Check again
50	140. Word Break II	Python, Swift	Art 1, Art 2	Hard	OHH Boy, you must recheck this, Important. TODO: Check again. An unique combination of DP, DFS and Backtracking
51	1027. Longest Arithmetic Sequence	Python, Swift	Art 1, Art 2	Medium	I didn't know that map can be used in 1d bottom-up dp. learned new things
52	304. Range Sum Query 2D - Immutable	Python, Swift	Art 1, Art 2	Medium	very good question, classical
53	1477. Find Two Non-overlapping Sub-arrays Each With Target Sum	Python, Swift	Art 1, Art 2	Medium	Very interesting and deceiving and tricky problem. An unique combination of sliding window and DP
54	368. Largest Divisible Subset	Python, Swift	Official Solution	Medium	Interesting problem.
55	523. Continuous Subarray Sum	Python, Swift	Art 1	Medium	Tricky to see the DP
56	689. Maximum Sum of 3 Non-Overlapping Subarrays	Python, Swift	Art 1	Hard	Mainly, tricly array index manipulation. TODO: need to solve it in DP and sliding window approach
57	338. Counting Bits	Python, Swift		Medium	---
58	1269. Number of Ways to Stay in the Same Place After Some Steps	Python, Swift	Art 1	Hard	Loved the problem. Very versatile
59	1277. Count Square Submatrices with All Ones	Python, Swift	Must	Medium	---

17. Bit Manipulation

Follow this golden rule to approach any DP problem.

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	78. Subsets	Python	Video 1, Video 2, Video 3	Medium	📌 TODO: code it in all 4 ways. First complete DFS, BFS, Bit Manipulation and some easy back tracking problem. ⭐ 😭 Didn't understand, check again
02	187. Repeated DNA Sequences	Python	Official	Medium	⭐ 😭 Didn't understand, check again
03	461. Hamming Distance	Python	---	Easy	📌 The key here is to practice bit operation, i ignore any other attempts
04	371. Sum of Two Integers	Python	Video 1, Atricle 1	Easy	📌 The key here is to practice bit operation, i ignore any other attempts
05	169. Majority Element	Python	Atricle 1	Easy	📌 The key here is to practice bit operation, i ignore any other attempts
06	191. Number of 1 Bits	Python	Article 1	Easy	📌 The key here is to practice bit operation
07	268. Missing Number	Python	Educative.io, Official	Easy	📌 Learned few very important binary logic properties. Also check cyclic sort technique
08	389. Find the Difference	Python	---	Easy	📌
09	231. Power of Two	Python	Official, Signed number representations	Easy	📌 Learned few very important binary logic properties
10	136. Single Number	Python	Educative.io	Easy	📌 The key here is to practice bit operation, i ignore any other attempts
11	137. Single Number II	Python	1, 2, 3, Check discussion	Medium	⭐ 😭 Didn't understand, check again
12	260. Single Number III	Python	Educative.io	Medium	⭐ Check again, very important
13	476. Number Complement	Python	Educative.io	Easy	⭐ Check again
14	832. Flipping an Image	Python	Educative.io	Easy	⭐ Check again
15	67. Add Binary	Python, Swift	Official, Art 1, Art 2, Vid 1, Vid 2	Easy (FUCK NO)	⭐ Check again

18. Miscellaneous (Line Swap, Binary Indexed Tree, Segment Tree, Minimax, Math, AVL Tree, Red-Black Tree, Interval Tree etc)

Leetcode problems with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	218. The Skyline Problem	Python, Swift	Vid 1, Vid 2, Vid 3, Vid 4, Art 1	Hard	TODO: Not Done. Very important.
02	375. Guess Number Higher or Lower II	Python, Swift	Art 0, Art 1, Art2 2, Art 3	Hard	TODO: Not Done. Very important. Did't understand properly
03	843. Guess the Word	Python	Art 1	Hard	Minimax. TODO: Check again. Very important and interesting
04	593. Valid Square	Python	Art 1, Art 2	Medium	Math
05	1272. Remove Interval	Python	Art 1	Medium	Line Swap
06	1288. Remove Covered Intervals	Python	Art 1	Medium	Line Swap with Greedy. A must read solution. A gold mie, learned a lot
07	1229. Meeting Scheduler	Python	Art 1	Medium	Line Swap, learned a lot
08	850. Rectangle Area II	Python	Art 1, Vid 1, Art 2	Hard	Line Swap using heap and Segment Tree. TODO: Solve it using Segment Tree
09	307. Range Sum Query - Mutable	Python	Vid 1, Art 1, Art 2	Medium	Segment Tree Basics. Very Important
10	327. Count of Range Sum	Python	Vid 1, Art 1, Art 2	Hard	Segment Tree Basics. Very Important
11	239. Sliding Window Maximum	Python	Video 1, Official, Art 1, Art 2, Art 3, Art 4	Hard	📌 Here, I have specifically focused on solving it with AVL and Red-Black Tree. A "Queue" approach can be found o Queue section
12	398. Random Pick Index	Python	Video 1, Art 1, Art 2, Art 3, Art 4, Art 5	Medium (Really!!??)	📌 Reservoir sampling, What's the point of asking this into an interview!!??
13	319. Bulb Switcher	Python	Art 1, Art 2, Art 3	Medium (Really!!??)	Are you fucking kidding me!! We are programmers, not math wizard.
14	1344. Angle Between Hands of a Clock	Python, Swift	---	Medium	FB really likes to ask tricky question.
15	1276. Number of Burgers with No Waste of Ingredients	Python, Swift	Art 1, Art 2, Art 3	Medium	Pure math
16	777. Swap Adjacent in LR String	Python, Swift	Art 1	Medium	Brainteser

---

---

AlgoExpert

100 Problems

My certificate of completion

1. Arrays

Problem statement from AlgoExpert.io with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	Two_Number_Sum	Swift, Python
02	Three_Number_Sum	Python
03	Smallest_Difference	Python
04	Four_Number_Sum	Python
05	Subarray_Sort	Python
06	Largest_Range	Python
07	Min_Rewards	Python
08	Zigzag_Traverse	Python
08	Apartment_Hunting	Python
09	Calendar_Matching	Python
10	Spiral_Traverse	Python
11	Monotonic_Array	Python
12	Move_Element_To_End	Python
13	Longest_Peak	Python

2. Binary Search Tree

Problem sstatement from AlgoExpert.io with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	BST_Construction_Iterative	Python
02	BST_Construction_Recursive	Python
03	Validate_BST	Python
04	Find_Closest_Value_in_BST	Python
05	BST_Traversal	Python
06	Same_BSTs	Python

3. Binary Tree

Problem sstatement from AlgoExpert.io with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	Invert_Binary_Tree	Python
02	Max_Path_Sum_In_Binary_Tree	Python
03	Iterative_In-order_Traversal	Python
04	Right_Sibling_Tree	Python
05	Branch_Sums	Python
06	Flatten_Binary_Tree	Python

4. Dynamic Programming

Problem statement from AlgoExpert.io with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	Number_Of_Ways_To_Make_Changes	Python
02	Minimum_Number_Of_Coins_For_Change	Python
03	Levenshtein_Distance	Python
04	Min_Number_Of_Jumps	Python	Video 1
05	Max_Sum_Increasing_Subsequence	Python
06	Longest_Common_Subsequence	Python	Video 1
07	Water_Area	Python
08	Knapsack_Problem	Python
09	Disk_Stacking	Python
10	Numbers_In_Pi	Python
11	Maximum_Subset_Sum_With_No_Adjacent_Element	Python
12	Max_Profit_With_K_Transactions	Python
13	Palindrome_Partitioning_Min_Cuts	Python
14	Longest_Increasing_Subsequence	Python	Video 1, Video 2, , Video 3
15	Longest_String_Chain	Python	---

5. Famous Algorithm

Problem statement from AlgoExpert.io with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	Kadane's_Algorithm	Python
02	Topological_Sort	Python
03	KMP_Algorithm	Python

6. Graphs

Problem sstatement from AlgoExpert.io with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	Youngest_Common_Ancestor	Python
02	Single_Cycle_Check	Python
03	River_Sizes	Python
04	Depth_First_Search	Python
05	Breadth_First_Search	Python
06	Boggle_Board	Python
07	Rectangle_Mania	Python
07	Airport_Connections	Python

7. Heaps

Problem sstatement from AlgoExpert.io with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	Min_Heap_Construction	Python	Video 1
02	Continuous_Median	Python	Video 1, Video 2

8. Linked List

Problem sstatement from AlgoExpert.io with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	Remove_Kth_Node_From_End	Python
02	Linked_List_Construction	Python
03	Find_Loop	Python
04	Reverse_Linked_List	Python
05	LRU_Cache	Python
06	Merge_Linked_List	Python

9. Recursion

Problem sstatement from AlgoExpert.io with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	Powerset	Python
02	Permutations	Python
03	Nth_Fibonacci	Python
04	Product_Sum	Python
05	Lowest_Common_Manager	Python
06	Number_Of_Possible_Binary_Tree_Topologies	Python
07	Interweaving_Strings	Python
08	Number_Of_Binary_Tree_Topologies	Python

10. Searching

Problem sstatement from AlgoExpert.io with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	Search_In_Sorted_Matrix	Python
02	Find_Three_Largest_Number	Python
03	Binary_Search	Python
04	Shifted_Binary_Search	Python
05	Search_For_Range	Python
06	Quick_Select (Kth smallest/largest element)	Python

11. Sorting

Problem sstatement from AlgoExpert.io with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	Selection_Sort	Python
02	Insertion_Sort	Python
03	Bubble_Sort	Python
04	Quick_Sort	Python	Video 1
05	Heap_Sort	Python
06	Merge_Sort	Python

12. Stacks

Problem sstatement from AlgoExpert.io with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	Balanced Bracket	Python
02	Min_Max_Stack_Construction	Python

13. String

Problem statement from AlgoExpert.io with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	Palindrom_Check	Python
02	Longest_Palindromic_Substring	Python
03	Caesar_Cipher_Encryptor	Python
04	Longest_Substring_Without_Duplication	Python
05	Underscorify_Substring	Python	---	Hard	TODO: Check again. Difficult to analyse the space ad time complexity
06	Pattern_Matcher	Python
07	Smallest_Substring_Containing	Python
08	Group_Anagrams	Python

14. Tries

Problem sstatement from AlgoExpert.io with solutions and tutorials/videos

#	Title	Solution	Tutorial	Level	Remarks
01	Suffix_Trie_Construction	Python
02	Multi_String_Search	Python

---

---

References

Some helpful links, channels, tutorials, blogs.

1. Strategies

Check this Golden posts first.

• Comprehensive Data Structure and Algorithm Study Guide

1. How a Googler solves coding problems
2. Nail Every Coding Interview by Becoming Asymmetrical
3. How to get into FAANG
4. Preparing for Programming interview with Python
5. The 30-minute guide to rocking your next coding interview
6. Google Interview Part-1 , Google Interview Part-2, Google Interview Part-3, Final Part
7. Amazon ও Google এ চাকরির সুযোগ পাওয়ার প্রস্তুতি পর্ব
8. How to use LeetCode effectively
9. How to solve ANY interview question
10. How To Ace The Google Coding Interview - Complete Guide
11. Software Engineering Interviews: The Golden Path To Passing
12. A MUST READ
13. 10 Steps to Solving a Programming Problem
14. Preparing to Apply or Interview at Google - Youtue playlist
15. Amazon ও Google এ চাকরির সুযোগ পাওয়ার প্রস্তুতি পর্ব
16. Coding Interviews
17. Tech Interview Handbook
18. Complete Introduction to the 30 Most Essential Data Structures & Algorithms
19. How to Solve Any Code Challenge or Algorithm

2. Courses/Books

1. Data Structures in Python: An Interview Refresher
2. Grokking the Coding Interview: Patterns for Coding Questions
3. Grokking Dynamic Programming Patterns for Coding Interviews
4. Coding Interview Class
5. Competitive Programmer’s Handbook

3. Swift

4. Python

Learn the following modules by heart. Just knowing all of the following items will made most of the problem one-liners.

1. itertools - Functions creating iterators for efficient looping - They will help you, more often than you think
   • Iterators and Iterables - What Are They and How Do They Work?
   • Itertools Module - Iterator Functions for Efficient Looping
2. collections - High-performance container datatypes - Believe me, this is pretty awesome
3. heapq - Heap queue algorithm - Obviously, we don't have to hand-code heaps anymore
4. bisect - Array bisection algorithm - Binary Search, simplified
5. Set
6. Dict - Now on, hash Tables are fun to work with
7. Sorting - Don't participate in competitions without reading this completely.
8. Start using lambda extensively
   • Lambda Expressions & Anonymous Functions
   • Map, Filter, and Reduce Functions
   • Lambda, filter, reduce and map
9. functools
10. Apart from these, all the builtin methods of default containers.
    • Strings and Character Data in Python
11. Understanding slice notation - you will need/use it more than you can imagine
12. Magic Methods

5. Channels

1. Tushar Roy - Coding Made Simple
2. Back To Back SWE
3. William Fiset
4. Irfan Baqui

6. Tree (Binary Tree, BST, AVL, Red-Black, B-Tree, B+ Tree, Segment Tree, Interval Tree, Range Tree, BIT, N-aray Tree, Trie etc)

Tree Basics (or not so basics)

1. Binary Tree playlist - Tushar Roy - Coding Made Simple
2. 8 Useful Tree Data Structures Worth Knowing
3. Segment Tree Range Minimum Query
4. Exploring Segment Trees
5. AVL Tree - Insertion and Rotations
6. B Trees and B+ Trees. How they are useful in Databases
7. Red Black Tree Insertion --- NOTE: Partho, read this
8. Fenwick Tree or Binary Indexed Tree
9. Fenwick Tree ( Binary Index Tree ) --- NOTE: Partho, read this

Binary Indexed Tree Vs Fenwick Tree

1. Fenwick Tree or Binary Indexed Tree - youtube
2. Binary Indexed Tree or Fenwick Tree - geeksforgeeks
3. Binary Indexed Tree or Fenwick Tree - topcoder
4. Segment Tree Range Minimum Query - youtube
5. Segment Tree | Set 1 (Sum of given range) - geeksforgeeks
6. Practical Data Structures for Frontend Applications: When to use Segment Trees
7. What is the difference between a binary indexed tree and a segment tree?
8. How does one decide when to use a Segment Tree or Fenwick Tree?
9. What are the differences between segment trees, interval trees, binary indexed trees and range trees?
10. Height, Depth and Level of a Tree
11. What is the difference between tree depth and height?

Self Balancing Binary Search Trees

1. Self-balancing binary search tree
2. Self-Balancing-Binary-Search-Trees (Comparisons)
3. Self-Balancing Binary Search Trees 101
4. 10.1 AVL Tree - Insertion and Rotations
5. Red Black tree | Introduction to Red Black trees | Data structure
6. Red Black Tree Insertion
7. Title
8. Title
9. Title

Augmented Binary Search Trees(Interval BS Vs Segment Tree Vs Range Tree)

1. Interval Search Trees - video
2. Interval Tree
3. What are the differences between segment trees, interval trees, binary indexed trees and range trees?
4. Interval Trees: One step beyond BST
5. Title
6. Title

7. Graph(Dijkstra, Union Find, Kruskal, Prim's, Minimum Spanning Tree, Topological Ordering...etc)

1. Graph Theory Playlist
2. Graph Theory Playlist 2
3. Union Find [Disjoint Set] Playlist
4. Disjoint Sets Data Structure - Weighted Union and Collapsing Find
5. Codinginterviewclass.com
6. Single(Di-Bel)/All(Flo) Source Shortest Path Algorithms: Dijkstra (1, 2), Bellman-Ford(1, 2), Floyd–Warshall(1, 2)
7. Dijkstra’s Algorithm Vs Bellman-Ford Algorithm Vs Floyd Warshall Algorithm ( 1, 2, 3 )
8. Minimum Spanning Tree Algorithm: Prim's ( 1, 2, Kruskal's (1, 2 )
9. Kruskal's algorithm Vs Prim's algorithm ( 1, 2, 3 )
10. Tushar Roy - Coding Made Simple - Grapy Algorithm Playlist

8. Bit Manipulation

1. Bit Manipulation - youtube
2. Conversion of Binary, Octal and Hexadecimal Numbers
3. Your guide to Bit Manipulation
4. Python Bitwise Operators
5. Add Two Numbers Without The "+" Sign (Bit Shifting Basics)
6. Binary Arithmetic
7. 1’s and 2’s complement of a Binary Number
8. What is “2's Complement”?
9. Bits manipulation (Important tactics)
10. Bit Manipulation
11. Python Bitwise Operators
12. XOR - The magical bitwise operator
13. A summary: how to use bit manipulation to solve problems easily and efficiently - leetcode
14. Bit Manipulation 4% of LeetCode Problems
15. Coding Interview University - Bitwise operations
16. Mask (computing)
17. What is Bit Masking?
18. Understanding Bit masks
19. Bitmasks: A very esoteric (and impractical) way of managing booleans
20. Hacker’s Delight - BOOK
21. Bitwise operators — Facts and Hacks
22. Signed number representations
23. Vid 1, Vid 2

9. Dynamic Programming

1. The FAST method
2. A good approach to attack DP
3. Tabulation vs Memoization
4. Memoization vs Tabulation
5. 1D Subproblems vs. 2D Subproblems
6. Memoization (1D, 2D and 3D)
7. Introduction to Multi-dimensional Dynamic Programming
8. Dynamic Programming Patterns - MUST READ
9. My experience and notes for learning DP
10. DP IS EASY! 5 Steps to Think Through DP Questions
11. Dynamic Programming Patterns

10. Greedy

1. Greedy Method - Introduction
2. Introduction to Greedy Method
3. Introduction to Greedy Algorithms | GeeksforGeeks
4. Basics of Greedy Algorithms
5. When to try greedy algorithms on problems?
6. How to spot a “greedy” algorithm?

11. DP VS Greedy

1. Greedy Algorithm and Dynamic Programming
2. Greedy approach vs Dynamic programming
3. What is the difference between dynamic programming and greedy approach?

12. Backtracking

1. Backtracking - wiki
2. Backtracking | Introduction
3. Introduction to Backtracking - Brute Force Approach
4. Branch and Bound Introduction
5. The Backtracking Blueprint: The Legendary 3 Keys To Backtracking Algorithms
6. Backtracking explained
7. Foundation of algorithms - Chapter 5 (Backtracking) notes
8. Backtracking Search Algorithms

13. Recursion

1. Learning to think with recursion, part 1
2. Learning to think with recursion, part 2
3. What makes a data structure recursive?
4. Binary Tree as a Recursive Data Structure
5. Recursion Visualizer - use Viz Mode
6. Thinking Recursively in Python
7. Breaking out of a recursive function?
8. Why does recursion return the first call in the stack and not the last?

14. Game Theory

1. Intuition for Solving a MiniMax Problems
2. Game theory — Minimax
3. How to make your Tic Tac Toe game unbeatable by using the minimax algorithm

15. Few special DS

1. Monotonic Queue Explained with LeetCode Problems