| 2. Add Two Numbers | Easy | 2 Approaches: Iteration and Recursion |
| 3. Longest Substring Without Repeating Characters | Easy | Two Pointers: Sliding Window with HashSet |
| 11. Container With Most Water | Medium | 2 Approaches: Brute Force and Two Pointers with Image Explanation |
| 17. Letter Combinations of a Phone Number | Medium | 4 Approaches: BF 4 Loops, Backtracking, BFS, Queue with Image Explaination |
| 19. Remove Nth Node From End of List | Medium | 3 Approaches: Brute Force, Stack, Slow Fast Pointers with Animation |
| 21. Merge Two Sorted Lists | Easy | The Recursive Algorithm with Detailed Image Explanation |
| 29. Divide Two Integers | Medium | 5 Approaches: BF use Long, BF use Int, Binary Search use Long, Binary Search use Int and Recursion |
| 31. Next Permutation | Medium | Two Pointers Solution with Detailed Explanation and Code Commented |
| 34. Find First and Last Position of Element in Sorted Array | Medium | Binary Search Twice |
| 36. Valid Sudoku | Medium | 2 Approaches: HashSet and Array |
| 39. Combination Sum | Medium | Easy Backtracking Approach: Deduplicating and Pruning |
| 42. Trapping Rain Water | Hard | From Brute Force to DP then Two Pointers with Detail Explaination |
| 43. Multiply Strings | Medium | Math Geek: Fast Fourier Transform and Number Theoretic Transform |
| 47. Permutations II | Medium | Permutation Problems: Backtracking and Pruning |
| 50. Pow(x, n) | Medium | Fast Power Algorithm: Binary Exponentiation |
| 55. Jump Game | Medium | Leetcode Jump Game Problems Series |
| 62. Unique Paths | Medium | 3 Approaches: DP, Recursion, Math |
| 69. Sqrt(x) | Medium | 4 Approaches: Brute Force, Exponent, Binary Search and the Newton Iteration Method |
| 70. Climbing Stairs | Easy | 9 Fibonacci Algorithms: the Most Complete Solutions All In One |
| 71. Simplify Path | Medium | Stack Solution with Easy Detailed Explanation |
| 74. Search a 2D Matrix | Medium | 6 Approaches: Brute Force, Row Search, Column Search, One Binary Search, 2D Coordinate Axis |
| 81. Search in Rotated Sorted Array II | Medium | Binary Search: The Key is Narrow the Search Interval Step by Step |
| 88. Merge Sorted Array | Easy | 3 Approaches: Sorting, Two Pointers and Reverse Two Pointers |
| 98. Validate Binary Search Tree | Medium | 3 Approaches: Recursion, DFS and Iteration |
| 102. Binary Tree Level Order Traversal | Medium | Java Simple BFS Solution |
| 114. Flatten Binary Tree to Linked List | Medium | Image Explanation to Understand the Recursion Solution |
| 117. Populating Next Right Pointers in Each Node II | Medium | 3 Approaches: BFS, BFS + LinkedList, Recursion |
| 118. Pascal's Triangle | Easy | Math Intuition of Dynamic Programming: Shift One and Added |
| 120. Triangle | Medium | Dynamic Programming Space O(n) Solutions: Top-Down and Bottom-Up Approaches |
| 125. Valid Palindrome | Easy | Simple Two Pointers Solution |
| 136. Single Number | Easy | The XOR Cheat Sheet and Bit Manipulation with Easy Detailed Explanation |
| Binary and N-ary Tree Traversal: 144. Binary Tree Preorder Traversal | Easy | Tree Traversals All In One: PreOrder, InOrder and PostOrder |
| 160. Intersection of Two Linked Lists | Easy | 2 Approaches: HashSet and Two Pointers with Detailed Explanation |
| 167. Two Sum II - Input Array Is Sorted | Medium | 4 Approaches: Brute Force, HashMap, Binary Search, Two Pointers |
| 171. Excel Sheet Column Number | Easy | 2 Approaches: Base Conversion from High to Low and from Low to High |
| 191. Number of 1 Bits | Easy | 6 Approaches: Cycle, API, Divide and Conquer, Low Bit, Bit Set, Recursion |
| 199. Binary Tree Right Side View | Medium | 2 Approaches: DFS and BFS with Detailed Explanation |
| 215. Kth Largest Element in an Array | Medium | 3 Approaches: Sorting, Priority Queue, Divide and Conquer |
| 216. Combination Sum III | Medium | 2 Approaches: Backtracking and Bit Mask |
| 219. Contains Duplicate II | Easy | 3 Approaches: Brute Force, HashMap and Sliding Window |
| 240. Search a 2D Matrix II | Medium | 5 Approaches: Brute Force, Binary Search(Row), Binary Search(Diagonal, Row, Col), Binary Search(Global), 2D Coord Axis |
| 242. Valid Anagram | Easy | 3 Approaches: HashMap, Sorting and Counting |
| 268. Missing Number | Easy | 4 Approaches: Sorting, Hash, XOR, Math |
| 278. First Bad Version | Easy | Java Binary Search Solution |
| 287. Find the Duplicate Number | Medium | 9 Approaches：Brute Force, Count, Hash, In-place Marked, Sorting, Index Sort, Binary Search, Bit Manipulation, Fast Slow Pointers |
| 295. Find Median from Data Stream | Medium | Two Heaps with the Follow Up's Solution |
| 300. Longest Increasing Subsequence | Medium | 3 Approaches: Backtrack, DP, Binary Search |
| 316. Remove Duplicate Letters | Medium | The Detailed Explanation with 3-Steps to Understand the Stack Approach |
| 322. Coin Change | Medium | 3 Approaches: DFS, BFS, DP |
| 329. Longest Increasing Path in a Matrix | Hard | 4 Approaches: BFS, Memory + DFS, DP, Topological Sorting |
| 334. Increasing Triplet Subsequence | Medium | Why Greedy works? |
| 341. Flatten Nested List Iterator | Medium | 2 Approaches: DFS and Iteration(Using Stack) |
| 342. Power of Four | Easy | Just One Line Code and Detailed Explanation |
| 344. Reverse String | Easy | 2 Approaches: Two Pointers and Recursion |
| 350. Intersection of Two Arrays II | Easy | 2 Approaches: Sorting with Two Pointers and HashMap |
| 372. Super Pow | Medium | 2 Approaches: Brute Force and Binary Exponentiation |
| 377. Combination Sum IV | Medium | 2 Approaches: Backtrack and DP with Follow Up Analysis |
| 378. Kth Smallest Element in a Sorted Matrix | Medium | 3 Approaches: Sorting, Merge Sort, Binary Search |
| 380. Insert Delete GetRandom O(1) | Medium | Data Structures: Thought Process from HashMap to HashMap + Array |
| 399. Evaluate Division | Medium | 4 Approaches: BFS, DFS, Floyd, Union Find |
| 406. Queue Reconstruction by Height | Medium | Pattern of Data Pairs Problem: Sorting First then Greedy |
| 429. N-ary Tree Level Order Traversal | Medium | Traverse the Tree Level by Level: Standard BFS Solution |
| 456. 132 Pattern | Medium | 4 Approaches: BF O(n^3), BF O(n^2), TreeMap, Monotonic Stack |
| 509. Fibonacci Number | Easy | 9 Fibonacci Algorithms: the Most Complete Solutions All In One with Image Explanation |
| 617. Merge Two Binary Trees | Easy | 4 Approaches: Recursion, Iteration, BFS and DFS |
| 658. Find K Closest Elements | Medium | 4 Approaches: Two Pointers, Sorting, Priority Queue and Binary Search |
| 680. Valid Palindrome II | Easy | 3 Approaches: Brute Force, Recursion and Two Pointers |
| 692. Top K Frequent Words | Medium | 2 Approaches: HashMap + Sort and Priority Queue |
| 729. My Calendar I | Medium | 3 Approaches: Brute Force, Binary Search, Segment Tree |
| 746. Min Cost Climbing Stairs | Easy | Fibonacci Numbers: 9 Approaches: Recursion, DP, Math, Matrix |
| 763. Partition Labels | Medium | Greedy Solution with Easy Detailed Explanation |
| 856. Score of Parentheses | Medium | The Tricky and Clean Solution: Replace Core by 1 |
| 858. Mirror Reflection | Medium | What If the Ray Not Reflected and Expand the Room with Image Explanation |
| 881. Boats to Save People | Medium | Greedy: Let the Heaviest Match the Lightest, if Not Matched, Let it Alone |
| 895. Maximum Frequency Stack | Hard | HashMap Solution with Detailed Explanation |
| 923. 3Sum With Multiplicity | Medium | 5 Approaches: BF, Three Pointers, TreeMap, Count, DP |
| 946. Validate Stack Sequences | Medium | 4 Approaches: Stack, Array, Greedy and O(n) Time O(1) Space |
| 947. Most Stones Removed with Same Row or Column | Medium | It is Literally a Graph: DFS and Union Find) |
| 991. Broken Calculator | Medium | Greedy: Reverse Thinking with Binary Algorithm |
| 1029. Two City Scheduling | Medium | Greedy: Sorting the Costs Array by What? |
| 1091. Shortest Path in Binary Matrix | Medium | Why Use BFS? Search Every Possible Path vs Search A Possible Path |
| 1137. N-th Tribonacci Number | Easy | Any Language Beats 100% with Time O(1) Solution |
| 1249. Minimum Remove to Make Valid Parentheses | Medium | Stack Solution with Easy Detailed Explanation |
| 1302. Deepest Leaves Sum | Medium | 2 Approaches: BFS(Level Order Travesal) and DFS(Get Max Depth, then Traversal) |
| 1631. Path With Minimum Effort | Medium | 3 Approaches: BFS(Dijkstra), Binary Search, Union Find |
| 1641. Count Sorted Vowel Strings | Medium | Image Explanation: Distributing N Balls into 5 Boxes, Some Boxes May Be Empty |
| 1642. Furthest Building You Can Reach | Medium | Priority Queue + Greedy: Consider Ladder as a One-time Unlimited Bricks |
| 1663. Smallest String With A Given Numeric Value | Medium | Greedy O(n) Solution with Image Explaination |
| 1721. Swapping Nodes in a Linked List | Medium | 3 Approaches: Swapping Values and Swapping Nodes with Image Explanation |
| 1780. Check if Number is a Sum of Powers of Three | Easy | 3 Approaches: Tricky, Recursive and Base 3 Conversion |
| 1834. Single-Threaded CPU | Medium | How to Maintain the Enqueued Tasks? Sorting the array then Priority Queue |
| 2215. Find the Difference of Two Arrays | Easy | Java HashSet Solution |
| 2475. Number of Unequal Triplets in Array | Easy | The Fastest O(n) Solution: Math Combinations |
