- binary search
- two pointer
- 11. Container With Most Water
- 15. 3Sum
- 18. 4Sum ## this question is the general answer for all n sum questions
- 19. Remove Nth Node From End of List
- 82. Remove Duplicates from Sorted List II
- 234. Palindrome Linked List
- 844. Backspace String Compare
- 986. Interval List Intersections
- sliding window
- breadth first search / depth first search
- 117. Populating Next Right Pointers in Each Node II tree, BAM!!!
- 130. Surrounded Regions
- 200. Number of Islands
- 210. Course Schedule II topological sort
- 417. Pacific Atlantic Water Flow
- 547. Number of Provinces
- 572. Subtree of Another Tree geee... tree is fucking hard
- 797. All Paths From Source to Target
- 815. Bus Routes hard, but smart one
- 967. Numbers With Same Consecutive Differences
- 1091. Shortest Path in Binary Matrix one very interesting solution - A* search
- recursion / backtracking
- dynamic programming
- 5. Longest Palindromic Substring
- 45. Jump Game II
- 55. Jump Game
- 62. Unique Paths
- 91. Decode Ways
- 121. Best Time to Buy and Sell Stock
- 139. Word Break
- 213. House Robber II
- 300. Longest Increasing Subsequence
- 376. Wiggle Subsequence
- 413. Arithmetic Slices
- 714. Best Time to Buy and Sell Stock with Transaction Fee here write the general method for the series of questions
- 1155. Number of Dice Rolls With Target Sum
- 1770. Maximum Score from Performing Multiplication Operations 2D DP
- bit manipulation
- 136. Single Number use of XOR, x ^ x = 0, 0 ^ x = x
- 231. Power of Two use of XOR
- 393. UTF-8 Validation
- linked list manipulation
- 23. merge k sorted list Use Min Heap, or divide and conquer
- 24. swap nodes in pair
- 25. Reverse Nodes in k-Group general solution for reversing the linked list
- 148. Sort List use merge sort
- tree structure
- 94. Binary Tree Inorder Traversal
- 108. Convert Sorted Array to Binary Search Tree binary search tree
- 110. Balanced Binary Tree
- 112. Path Sum
- 173. Binary Search Tree Iterator similar idea to 230 for dfs solution, hard question
- 226. Invert Binary Tree
- 230. Kth Smallest Element in a BST
- 429. N-ary Tree Level Order Traversal
- 437. Path Sum III difficult one!!!
- 543. Diameter of Binary Tree
- 606. Construct String from Binary Tree
- 623. Add One Row to Tree
- 637. Average of Levels in Binary Tree
- 814. Binary Tree Pruning
- 987. Vertical Order Traversal of a Binary Tree
- 1448. Count Good Nodes in Binary Tree DFS
- 1457. Pseudo-Palindromic Paths in a Binary Tree
- greedy
- 334. Increasing Triplet Subsequence
- 435. Non-overlapping Intervals
- 621. Task Scheduler really tricky, difficult to explain
- 1578. Minimum Time to Make Rope Colorful
- 2131. Longest Palindrome by Concatenating Two Letter Words
- heap (priority queue)
- questions from expedia.py
- 692. Top K Frequent Words
- others
- 8. String to Integer (atoi) DFA (deterministic finite automata)
- 59. Spiral Matrix II matrix manipulation
- 202. Happy Number use Floyd's Cycle detection
- 238. Product of Array Except Self prefix product and suffix product
- 336. Palindrome Pairs hash
- 378. kth smallest in sorted matrix use heap for log(N) insertion
- 560. Subarray Sum Equals K prefix sum + hashmap, really really brilliant
- 609. Find Duplicate File in System use hash
- 706. Design HashMap implement a hashmap
- 990. Satisfiability of Equality Equations union find
- 1061. Lexicographically Smallest Equivalent String union find