Study Notes for NeetCode 150 Problems

Contains Duplicate

• hash map
• iterate nums, flag map[num] or just make count, check if map[num] is defined
• return true if map[num] !== undefined

Valid Anagram

• sort both, easy method
• hash map (optimal): check length, make count hash map of both
• iterate over one hash map's keys and check if map[key] === map2[key]
• for (const key in map)!!!!

Two Sum

• hash map
• iterate through array
• calc diff between target and current number
• check if it exists and is not the current index
• return diff's index and current index

Group Anagrams

• First Method Sorting

• hash map

• iterate through array of strings

• sort, push original string to map at sorted index

• return Object.values(map)

• Optimal Method Char Count

• hash map

• iterate through array of strings

• make array new array len 26 fill 0

• iterate through chars, fill char count "c.charCodeAt(0)"

• so same thing, joined char count array is key

• push og string to map

• return Object.values(map)

  Top K Frequent Elements

  • Easy Method Sorting w/ hash map
  • Make hash map with count
  • Turn map into array where each element is array with num and count
  • Sort array by count
  • return array of top k elements

  Longest Consecutive Sequence

  • Set
  • iterate set
  • if no num - 1, thats a set
  • continue while(num[n + streak))
  • keep track of longest

LeetCode Topics

Array

0001-two-sum

Hash Table

0001-two-sum