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LeetCode (370/1521) → Easy 131--Medium 193--Hard 46

Algorithm exercises 🚨🚨🚨

the following problem is choose by:

the problem of Daily Challenges and Weekly Contest, and the similar problem on leetcode.com and leetcode-cn.com.

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Book

• Algorithms, 4TH

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Tag	Progress
Array	105/261
Backtracking	15/55
Binary Indexed Tree	2/6
Binary Search	32/84
Binary Search Tree	2/15
Bit Manipulation	9/39
Brainteaser	3/5
Breadth-first Search	16/68
Concurrency	1/9
Database	3/112
Depth-first Search	39/95
Desigin	5/49
Divide and Conquer	6/19
Dynamic Programming	54/188
Geometry	2/7
Graph	9/42
Greedy	16/80
Hash Table	22/127
Heap	5/34
Linked List	27/38
Math	35/122
Memoization	1/1
Minimax	1/8
Queue	2/9
Recursion	5/15
Random	1/6
Segment Tree	3/12
Sliding Window	7/23
Sort	16/52
Stack	17/57
String	57/179
Topological Sort	4/7
Tree	54/137
Trie	3/17
Two Pointers	31/60
Union Find	5/29
other	5/?

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Title	Tags	Difficulty
1. Two Sum	Array HashTable	Easy
2. Add Two Numbers	Math LinkedList	Medium
3.Longest Substring Without Repeating Characters	String Two Pointers HashTables Sliding Window	Medium
4. Median of Two Sorted Arrays.md🚨	Array Binary Serach Divide and Conquer	Hard
5. Longest Palindromic Substring🚨	String Dynamic Programming	Medium
6. ZigZag Conversion	String	Medium
7. Reverse Integer	Math	Easy
8. String to Integer (atoi)	String Math	Medium
9. Palindrome Number	Math	Easy
10. Regular Expression Matching🚨	String Dynamic Programming BackTracking	Hard
11. Container With Most Water	Array Two Pointer	Medium
12. Integer to Roman	Math String	Medium
13. Roman to Integer	Math String	Easy
14. Longest Common Prefix	String	Easy
15. 3Sum 🚨	Array Two Pointer	Medium
16. 3Sum Closest	Array Two Pointer	Medium
17. Letter Combinations of a Phone Number	String BackTracking	Medium
18. 4Sum 🚨	Array Two Pointer HashTable	Medium
19. Remove Nth Node From End of List	LinkedList Two Pointers	Medium
20. Valid Parentheses	String Stack	Easy
21. Merge Two Sorted Lists	LinkedList	Easy
22. Generate Parentheses	String BackTracking	Medium
23.Merge k Sorted Lists	LinkedList Divide and Conquer Heap	Hard
24. Swap Nodes in Pairs	LinkedList	Medium
25. Reverse Nodes in k-Group	LinkedList	Hard
26. Remove Duplicates from Sorted Array	Array Two Pointer	Easy
27. Remove Element	Array Two Pointer	Easy
28. Implement strStr()	String Two Pointers	Easy
31. Next Permutation 🚨	Array	Medium
32. Longest Valid Parentheses🚨	String Dynamic Programming	Hard
33. Search in Rotated Sorted Array 🚨	Array Binary Serach	Medium
34. Find First and Last Position of Element in Sorted Array 🚨	Array Binary Serach	Medium
35. Search Insert Position	Array Binary Serach	Easy
38. Count and Say	String	Easy
39. Combination Sum	Array Backtracking	Medium
40. Combination Sum II	Array Backtracking	Medium
41. First Missing Positive🚨	Array	Hard
43. Multiply Strings	Math String	Medium
44. Wildcard Matching	String Dynamic Programming Greedy Backtracking	Hard
49. Group Anagrams	String HashTable	Medium
50. Pow(x, n)	Math BinarySearch	Medium
54. Spiral Matrix	Array	Medium
58. Length of Last Word	String	Easy
60. Permutation Sequence	Math Backtracking	Medium
61. Rotate List	LinkedList Two Pointers	Medium
62. Unique Paths	Array Dynamic Programming	Medium
63. Unique Paths II	Array Dynamic Programming	Medium
64. Minimum Path Sum	Array Dynamic Programming	Medium
65. Valid Number	String Math	Hard
66. Plus One	Array	Easy
67. Add Binary	Math String	Easy
70. Climbing Stairs	Dynamic Programming	Easy
75. Sort Colors	Array Two Pointer Sort	Medium
78. Subsets	Array Backtracking Bit Manipulation	Medium
79. Word Search	Array BackTracking	Medium
82. Remove Duplicates from Sorted List II	LinkedList	Medium
83. Remove Duplicates from Sorted List	LinkedList	Easy
84. Largest Rectangle in Histogram	Array Stack	Hard
86. Partition List	LinkedList Two Pointers	Medium
91. Decode Ways	Dynamic Programming String	Medium
92. Reverse Linked List II	LinkedList	Medium
94. Binary Tree Inorder Traversal	Stack HashTable Tree	Medium
95. Unique Binary Search Trees II	Tree Dynamic Programming	Medium
96. Unique Binary Search Trees	Tree Dynamic Programming	Medium
97. Interleaving String	String Dynamic Programming	Hard
98. Validate Binary Search Tree	Tree DFS	Medium
100. Same Tree	DFS Tree	Easy
101. Symmetric Tree	DFS BFS Tree	Easy
102. Binary Tree Level Order Traversal	Tree BFS	Medium
103. Binary Tree Zigzag Level Order Traversal	Tree BFS Stack	Medium
104. Maximum Depth of Binary Tree	DFS Tree	Easy
105. Construct Binary Tree from Preorder and Inorder Traversal	Tree Array DFS	Medium
106. Construct Binary Tree from Inorder and Postorder Traversal	Tree Array DFS	Medium
107. Binary Tree Level Order Traversal II	Tree BFS	Easy
108. Convert Sorted Array to Binary Search Tree	DFS Tree	Easy
109. Convert Sorted List to Binary Search Tree	LinkedList DFS	Medium
112. Path Sum	DFS Tree	Easy
120. Triangle	Array Dynamic Programming	Medium
121. Best Time to Buy and Sell Stock	Array Dynamic Programming	Easy
122. Best Time to Buy and Sell Stock II	Array Greedy	Easy
123. Best Time to Buy and Sell Stock III	Array Dynamic Programming	Hrad
124. Binary Tree Maximum Path Sum	DFS Tree	Hard
125. Valid Palindrome	String Two Pointer	Easy
126. Word Ladder II 🚨	Array Backtracking String BFS	Hard
127. Word Ladder 🚨	BFS	Medium
128. Longest Consecutive Sequence 🚨	Array Union Find	Hard
129. Sum Root to Leaf Numbers	DFS Tree	Medium
130. Surrounded Regions	DFS BFS Union Find	Medium
136. Single Number	HashTable Bit Manipulation	Easy
137. Single Number II	Bit Manipulation	Medium
138. Copy List with Random Pointer	LinkedList HashTable	Medium
139. Word Break	Dynamic Programming	Medium
140. Word Break II	Dynamic Programming Backtracking	Hard
141. Linked List Cycle	LinkedList Two Pointers	Easy
142. Linked List Cycle II	LinkedList Two Pointers	Medium
143. Reorder List	LinkedList	Medium
144. Binary Tree Preorder Traversal	Stack Tree	Medium
145. Binary Tree Postorder Traversal	Tree Stack	Hard
151. Reverse Words in a String	String	Medium
153. Find Minimum in Rotated Sorted Array	Array BinarySearch	Medium
154. Find Minimum in Rotated Sorted Array II	Array BinarySearch	Hard
155. Min Stack	Stack Design	Easy
167. Two Sum II - Input array is sorted	Array Two pointers Binary Search	Easy
169. Majority Element	Array Divide and Conquer Bit Manipulation	Easy
173. Binary Search Tree Iterator	Tree Stack Design	Medium
174. Dungeon Game	Dynamic Programming Binary Search	Hard
188. Best Time to Buy and Sell Stock IV	Dynamic Programming	Hard
189. Rotate Array	Array	Easy
190. Reverse Bits	Bit Manipulation	Easy
198. House Robber	Dynamic Programming	Easy
203. Remove Linked List Elements	LinkedList	Easy
204. Count Primes	Math HashTable	Easy
206. Reverse Linked List	LinkedList	Easy
207. Course Schedule	DFS BFS Graph Topological Sort	Medium
208. Implement Trie (Prefix Tree)	Trie Design	Medium
209. Minimum Size Subarray Sum	Array Two Pointer Binary Search	Medium
210. Course Schedule II	DFS BFS Graph Topological Sort	Medium
212. Word Search II	Trie Backtracking	Hard
215. Kth Largest Element in an Array 🚨	Divide and Conquer Heap	Medium
216. Combination Sum III	Array Backtracking	Medium
217. Contains Duplicate	Array HashTable	Easy
221. Maximal Square	Dynamic Programming	Medium
222. Count Complete Tree Nodes	Tree Binary Search	Medium
226. Invert Binary Tree	Tree	Easy
230. Kth Smallest Element in a BST	Binary Search Tree	Medium
231. Power of Two	Math Bit Manipulation	Easy
237. Delete Node in a Linked List	LinkedList	Easy
238. Product of Array Except Self	Array	Medium
258. Add Digits	Math	Easy
260. Single Number III	Bit Manipulation	Medium
263. Ugly Number	Math	Easy
264. Ugly Number II	Math Dynamic Programming Heap	Medium
268. Missing Number	Array Math Bit Manipulation	Easy
274. H-Index	Sort HashTable	Medium
275. H-Index II	Binary Search	Medium
279. Perfect Squares 🚨	Dynamic Programming BFS Math	Medium
283. Move Zeroes	Array Two pointers	Easy
287. Find the Duplicate Number	Array Two pointers Binary Search	Medium
292. Nim Game	Brainteaser Minimax	Easy
297. Serialize and Deserialize Binary Tree	Tree Design	Hard
300. Longest Increasing Subsequence	Binary Search Dynamic Programming	Medium
303. Range Sum Query - Immutable	Dynamic Programming	Easy
307. Range Sum Query - Mutable	Binary Indexed Tree Segment Tree	Medium
309. Best Time to Buy and Sell Stock with Cooldown 🚨	Dynamic Programming	Medium
312. Burst Balloons 🚨	Divide and Conquer Dynamic Programming	Hard
315. Count of Smaller Numbers After Self	Binary Search Binary Indexed Tree Divide and Conquer Sort Segment Tree	Hard
319. Bulb Switcher	Math Brainteaser	Medium
322. Coin Change 🚨	Dynamic Programming	Medium
328. Odd Even Linked List	LinkedList	Medium
329. Longest Increasing Path in a Matrix	DFS TopologicalSort Memoization	Hard
332. Reconstruct Itinerary 🚨	DFS Graph	Medium
343. Integer Break	Math Dynamic Programming	Medium
344. Reverse String	String Two Pointers	Easy
347. Top K Frequent Elements	HashTable Heap	Medium
349. Intersection of Two Arrays	Binary Search Two Pointers HashTable Sort	Easy
350. Intersection of Two Arrays II	HashTable Two Pointers BinarySearch Sort	Easy
368. Largest Divisible Subset	Dynamic Programming Math	Medium
378. Kth Smallest Element in a Sorted Matrix	Binary Search Heap	Medium
392. Is Subsequence	Binary Search Dynamic Programming Greedy	Medium
394. Decode String	DFS Stack	Medium
406. Queue Reconstruction by Height	Greedy	Medium
410. Split Array Largest Sum	Binary Search Dynamic Programming	Hard
430. Flatten a Multilevel Doubly Linked List	LinkedList DFS	Medium
441. Arranging Coins	Math BinarySearch	Easy
442. Find All Duplicates in an Array	Array	Medium
445. Add Two Numbers II	LinkedList	Medium
448. Find All Numbers Disappeared in an Array	Array	Easy
461. Hamming Distance	Bit Manipulation	Easy
463. Island Perimeter	HashTable	Easy
468. Validate IP Address	String	Medium
485. Max Consecutive Ones	Array	Easy
494. Target Sum 🚨	Dynamic Programming DFS	Medium
495. Teemo Attacking	Array	Medium
496. Next Greater Element I	Stack	Easy
503. Next Greater Element II	Stack	Medium
509. Fibonacci Number	Array	Easy
513. Find Bottom Left Tree Value	DFS BFS Tree	Medium
515. Find Largest Value in Each Tree Row	DFS BFS Tree	Medium
518. Coin Change 2	Dynamic Programming	Medium
520. Detect Capital	String	Easy
521. Longest Uncommon Subsequence I	String	Easy
523. Continuous Subarray Sum 🚨	Math Dynamic Programming	Medium
525. Contiguous Array 🚨	HashTable	Medium
528. Random Pick with Weight 🚨	Random BinarySerach	Medium
530. Minimum Absolute Difference in BST	Tree	Easy
535. Encode and Decode TinyURL	Math HashTable	Medium
537. Complex Number Multiplication	Math String	Medium
539. Minimum Time Difference	String	Easy
556. Next Greater Element III	String	Medium
557. Reverse Words in a String III	String	Easy
559. Maximum Depth of N-ary Tree	DFS BFS Tree	Easy
561. Array Partition I	Array	Easy
565. Array Nesting	Array	Easy
566. Reshape the Matrix	Array	Easy
581. Shortest Unsorted Continuous Subarray	Array	Easy
589. N-ary Tree Preorder Traversal	Tree	Easy
595. Big Countries	Database	Easy
617. Merge Two Binary Trees	Tree	Easy
621. Task Scheduler	Array Greedy Queue	Medium
627. Swap Salary	Datebase	Easy
628. Maximum Product of Three Numbers	Array Math	Easy
630. Course Schedule III	Greedy	Hard
645. Set Mismatch	Math HashTable	Easy
654.Maximum Binary Tree	Tree	Medium
657. Judge Route Circle	String	Easy
661. Image Smoother	Array	Easy
662. Maximum Width of Binary Tree	Tree	Medium
667. Beautiful Arrangement II	Array	Medium
674. Longest Continuous Increasing Subsequence	Array	Easy
692. Top K Frequent Words	HashTable Heap Trie	Medium
695. Max Area of Island	Array DFS	Medium
697. Degree of an Array	Array	Easy
700. Search in a Binary Search Tree	Tree	Easy
701. Insert into a Binary Search Tree	Tree	Medium
709.To Lower Case	String	Easy
714. Best Time to Buy and Sell Stock with Transaction Fee	Array Dynamic Programming Greedy	Medium
717. 1-bit and 2-bit Characters	Array	Easy
718. Maximum Length of Repeated Subarray	Array BinarySearch HashTable Dynamic Programming	Medium
725. Split Linked List in Parts	LinkedList	Medium
726. Number of Atoms	HashTable Stack Recursion	Hard
728. Self Dividing Numbers	Math	Easy
739. Daily Temperatures	Stack HashTable	Medium
741. Cherry Pickup 🚨🚨🚨	Dynamic Programming	Hard
746. Min Cost Climbing Stairs	Array Dynamic Programming	Easy
763. Partition Labels	Greedy Two Pointers	Medium
766. Toeplitz Matrix	Array	Easy
769. Max Chunks To Make Sorted	Array	Medium
771. Jewels and Stones	HashTable	Easy
783. Minimum Distance Between BST Nodes	Tree Recursive	Easy
785. Is Graph Bipartite?	DFS BFS Graph	Medium
787. Cheapest Flights Within K Stops 🚨	Dynamic Programming DFS Heap	Medium
791. Custom Sort String	String	Medium
797. All Paths From Source to Target	DFS	Medium
804. Unique Morse Code Words	String	Easy
807. Max Increase to Keep City Skyline	other	Medium
814. Binary Tree Pruning	Tree	Medium
817. Linked List Components	LinkedList	Medium
824. Goat Latin	String	Easy
830. Positions of Large Groups	Array	Easy
832. Flipping an Image	Array	Easy
837. New 21 Game 🚨	Dynamic Programming	Medium
841. Keys and Rooms	DFS Graph	Medium
852. Peak Index in a Mountain Array	Binary Search	Easy
862. Shortest Subarray with Sum at Least K 🚨	Queue Binary Search	Hard
863. All Nodes Distance K in Binary Tree	Tree DFS BFS	Medium
872. Leaf-Similar Trees	DFS Tree	Easy
875. Koko Eating Bananas	BinarySearch	Medium
876. Middle of the Linked List	LinkedList	Easy
889. Construct Binary Tree from Preorder and Postorder Traversal	Tree	Medium
890. Find and Replace Pattern	String	Easy
894. All Possible Full Binary Trees🚨	Tree Recursion	Medium
897. Increasing Order Search Tree	DFS Tree	Easy
904. Fruit Into Baskets	Two Pointers	Medium
905. Sort Array By Parity	Array	Easy
925. Long Pressed Name	String Two Pointer	Easy
929. Unique Email Addresses	String	Easy
930. Binary Subarrays With Sum	Two Pointers HashTable	Medium
938. Range Sum of BST	Tree Recursion	Easy
942. DI String Match	Math	Easy
950. Reveal Cards In Increasing Order	Array	Medium
957. Prison Cells After N Days	HashTable	Medium
959. Regions Cut By Slashes	DFS Graph Union Find	Medium
961. N-Repeated Element in Size 2N Array		Easy
965. Univalued Binary Tree	Tree	Easy
974. Subarray Sums Divisible by K	Array HashTable	Medium
977.Squares of a Sorted Array	Array TwoPointers	Easy
978. Longest Turbulent Subarray	Array Dynamic Programming Silding Window	Medium
979. Distribute Coins in Binary Tree	DFS Tree	Medium
980. Unique Paths III	DFS BackTracking	Hard
983. Minimum Cost For Tickets 🚨	Dynamic Programming	Medium
990. Satisfiability of Equality Equations	Union Find Graph	Medium
992. Subarrays with K Different Integers	Two Pointers HashTable Sliding Window	Hard
1002. Find Common Characters	Array HashTable	Easy
1004. Max Consecutive Ones III	Two Pointers Sliding Window	Medium
1008. Construct Binary Search Tree from Preorder Traversal	Tree	Medium
1011. Capacity To Ship Packages Within D Days	Array Binary Search	Medium
1014. Best Sightseeing Pair 🚨	Array	Medium
1019. Next Greater Node In Linked List 🚨	LinkedList Stack	Medium
1021. Remove Outermost Parentheses	Stack	Easy
1025. Divisor Game	Math Dynamic Programming	Easy
1026. Maximum Difference Between Node and Ancestor	DFS Tree	Medium
1028. Recover a Tree From Preorder Traversal	DFS Tree	Hard
1029. Two City Scheduling	Greedy	Easy
1038. Binary Search Tree to Greater Sum Tree	Binary Search Tree	Medium
1044. Longest Duplicate Substring 🚨🚨🚨	Binary Search HashTable	Hard
1051. Height Checker	Array	Easy
1053. Previous Permutation With One Swap	Array Greedy	Medium
1079. Letter Tile Possibilities 🚨	BackTracking	Medium
1108.Defanging an IP Address	String	Easy
1109. Corporate Flight Bookings 🚨	Math Array	Medium
1110. Delete Nodes And Return Forest	DFS Tree	Medium
1115. Print FooBar Alternately	Concurrency	Medium
1122. Relative Sort Array	Array Sort	Easy
1130. Minimum Cost Tree From Leaf Values	Tree Stack Dynamic Programming	Medium
1137. N-th Tribonacci Number	Recursive	Easy
1143. Longest Common Subsequence	Dynamic Programming	Medium
1155. Number of Dice Rolls With Target Sum	Dynamic Programming	Medium
1179. Reformat Department Table🚨	Datebase	Easy
1207. Unique Number of Occurrences	HashTable	Easy
1221. Split a String in Balanced Strings	String	Easy
1234. Replace the Substring for Balanced String	String Two Pointers	Medium
1248. Count Number of Nice Subarrays	Two Pointers	Easy
1249. Minimum Remove to Make Valid Parentheses	String Stack	Medium
1252. Cells with Odd Values in a Matrix	Array	Easy
1261. Find Elements in a Contaminated Binary Tree	HashTable Tree	Medium
1266. Minimum Time Visiting All Points	Array Geometry	Easy
1281. Subtract the Product and Sum of Digits of an Integer	Math	Easy
1282. Group the People Given the Group Size They Belong To🚨	Greedy	Medium
1290.Convert Binary Number in a Linked List to Integer	LinkedList Bit Manipulation	Easy
1300. Sum of Mutated Array Closest to Target	Array BinarySearch	Medium
1302. Deepest Leaves Sum	DFS Tree	Medium
1314. Matrix Block Sum	Dynamic Programming	Medium
1315. Sum of Nodes with Even-Valued Grandparent	DFS Tree	Medium
1340. Jump Game V 🚨	Dynamic Programming	Hard
1344. Angle Between Hands of a Clock	Math	Medium
1358. Number of Substrings Containing All Three Characters	String	Medium
1419. Minimum Number of Frogs Croaking	String	Medium
1425. Constrained Subsequence Sum	Dynamic Programming	Hard
1431. Kids With the Greatest Number of Candies	Array	Easy
1446. Consecutive Characters	String	Easy
1450. Number of Students Doing Homework at a Given Time	Array	Easy
1451. Rearrange Words in a Sentence	String Sort	Medium
1452. People Whose List of Favorite Companies Is Not a Subset of Another List	String Sort	Medium
1455. Check If a Word Occurs As a Prefix of Any Word in a Sentence	String	Easy
1456. Maximum Number of Vowels in a Substring of Given Length	String Sliding Window	Medium
1457. Pseudo-Palindromic Paths in a Binary Tree	DFS Tree Bit Manipulation	Medium
1458. Max Dot Product of Two Subsequences 🚨	Dynamic Programming	Hard
1462. Course Schedule IV	Graph TopologicalSort	Medium
1464. Maximum Product of Two Elements in an Array	Array	Easy
1465. Maximum Area of a Piece of Cake After Horizontal and Vertical Cuts	DFS Tree	Medium
1466. Reorder Routes to Make All Paths Lead to the City Zero	DFS Tree	Medium
1470. Shuffle the Array	Array	Easy
1471. The k Strongest Values in an Array	Array Sort	Medium
1472. Design Browser History	Design	Medium
1473. Paint House III 🚨	Dynamic Programming	Hard
1480. Running Sum of 1d Array	Array	Easy
1481. Least Number of Unique Integers after K Removals	Array Sort	Medium
1482. Minimum Number of Days to Make m Bouquets 🚨🚨🚨	Binary Search Array	Medium
1483. Kth Ancestor of a Tree Node 🚨🚨	Dynamic Programming	Hard
1486. XOR Operation in an Array	Array Bit Manipulation	Easy
1487. Making File Names Unique	String HashTable	Medium
1488. Avoid Flood in The City	Array HashTable	Medium
1491. Average Salary Excluding the Minimum and Maximum Salary	Array Sort	Easy
1492. The kth Factor of n	Math	Medium
1493. Longest Subarray of 1's After Deleting One Element	Array	Medium
1496. Path Crossing	String	Easy
1497. Check If Array Pairs Are Divisible by k	Array Math Greedy	Medium
1498. Number of Subsequences That Satisfy the Given Sum Condition 🚨	Sort Sliding Window	Medium
1499. Max Value of Equation 🚨	Array Sliding Window	Hard
1502. Can Make Arithmetic Progression From Sequence	Array Sort	Easy
1503. Last Moment Before All Ants Fall Out of a Plank	Array Brainteaser	Medium
1504. Count Submatrices With All Ones	Dynamic Programming	Medium
1505. Minimum Possible Integer After at Most K Adjacent Swaps On Digits 🚨	Greedy	Hard
1507. Reformat Date	String	Easy
1508. Range Sum of Sorted Subarray Sums	Array Sort	Medium
1509. Minimum Difference Between Largest and Smallest Value in Three Moves	Array Sort	Medium
1510. Stone Game IV	Dynamic Programming	Hard
1512. Number of Good Pairs	Array Math HashTable	Easy
1513. Number of Substrings With Only 1s	String Math	Medium
1514. Path with Maximum Probability 🚨🚨🚨	Graph	Medium
1515. Best Position for a Service Centre 🚨🚨	Geometry	Hard
1518. Water Bottles	Greedy	Easy
1519. Number of Nodes in the Sub-Tree With the Same Label	BFS DFS	Medium
1520. Maximum Number of Non-Overlapping Substrings 🚨🚨	Greedy	Medium
1521. Find a Value of a Mysterious Function Closest to Target 🚨🚨🚨	BinarySearch Segment Tree Bit Manipulation	Hard
1523. Count Odd Numbers in an Interval Range	Math	Easy
1528. Shuffle String	Sort	Easy
1529. Bulb Switcher IV	String	Medium
1530. Number of Good Leaf Nodes Pairs	Tree DFS	Medium