| 1 |
Two Sum |
Easy |
HashMap |
| 2 |
Add Two Numbers |
Medium |
LinkedList |
| 3 |
Longest Substring Without Repeating Characters |
Medium |
Slide window |
| 4 |
Median of Two Sorted Arrays |
Hard |
LinkedList |
| 5 |
Longest Palindromic Substring |
Medium |
Array |
| 7 |
Reverse Integer |
Easy |
Array |
| 8 |
String to Integer (atoi) |
Medium |
Array |
| 9 |
Palindrome Number |
Easy |
String |
| 11 |
Container With Most Water |
Medium |
[Array |
| 14 |
Longest Common Prefix |
Easy |
String |
| 15 |
Three Sum |
Medium |
Array, double pointer |
| 16 |
3Sum Closest |
Medium |
Array, double pointer |
| 18 |
Four Sum |
Medium |
Array |
| 20 |
Valid Parentheses |
Easy |
Stack |
| 21 |
Merge Two Sorted Lists |
Easy |
LinkedList |
| 22 |
Generate Parentheses |
Medium |
Recursion |
| 23 |
Merge k Sorted Lists |
Hard |
LinkedList |
| 24 |
Swap Nodes in Pairs |
Medium |
LinkedList |
| 25 |
Reverse Nodes in k-Group |
Hard |
LinkedList |
| 26 |
Remove Duplicates from Sorted Array |
Easy |
Array |
| 33 |
Search in Rotated Sorted Array |
Medium |
Array, binary search |
| 36 |
Valid Sudoku |
Medium |
Prune |
| 37 |
Sudoku Solver |
Hard |
Prune |
| 43 |
Multiply Strings |
Medium |
Array, digit |
| 46 |
Permutations |
Medium |
Recursion |
| 50 |
Pow(x, n) |
Medium |
Recursion |
| 51 |
N-Queens |
Hard |
Prune |
| 52 |
N-Queens II |
Hard |
Prune |
| 53 |
Maximum Subarray |
Easy |
Dp |
| 59 |
Spiral Matrix II |
Medium |
Array |
| 61 |
Rotate List |
Medium |
LinkedList |
| 62 |
Unique Paths |
Medium |
Dp |
| 70 |
Climbing Stairs |
Easy |
Dp |
| 72 |
Edit Distance |
Hard |
Dp or recursion |
| 78 |
subsets |
Medium |
Recursion, backtrack |
| 82 |
Remove Duplicates from Sorted List II |
Medium |
LinkedList |
| 83 |
Remove Duplicates from Sorted List |
Easy |
LinkedList |
| 88 |
Merge Sorted Array |
Easy |
Array, double pointer |
| 89 |
Gray Code |
Medium |
Dp |
| 94 |
Binary Tree Inorder Traversal |
Medium |
Tree |
| 98 |
Validate Binary Search Tree |
Medium |
Tree |
| 102 |
Binary Tree Level Order Traversal |
Medium |
Tree |
| 104 |
Maximum Depth of Binary Tree |
Easy |
Tree |
| 105 |
Construct Binary Tree from Preorder and Inorder Traversal |
Medium |
Tree |
| 110 |
Balanced Binary Tree |
Easy |
Tree |
| 111 |
Minimum Depth of Binary Tree |
Easy |
Tree |
| 121 |
Best Time to Buy and Sell Stock |
Easy |
Dp, double pointer |
| 122 |
Best Time to Buy and Sell Stock II |
Easy |
Greedy |
| 124 |
Binary Tree Maximum Path Sum |
Medium |
Tree |
| 128 |
Longest Consecutive Sequence |
Hard |
Array, hashmap + dp |
| 129 |
Sum Root to Leaf Numbers |
Medium |
[Tree |
| 136 |
Single Number |
Easy |
Dp, XOR |
| 141 |
Linked List Cycle |
Easy |
LinkedList |
| 142 |
Linked List Cycle II |
Medium |
LinkedList |
| 144 |
Binary Tree Preorder Traversal |
Medium |
Tree, recursion, iteration |
| 146 |
LRU |
Medium |
Double linkedList, hash table |
| 148 |
Sort List |
Medium |
LinkedList, merge sort |
| 155 |
Min Stack |
Easy |
Stack |
| 160 |
Intersection of two linked lists |
Easy |
LinkedList |
| 169 |
Majority Element |
Easy |
Sort |
| 206 |
Reverse Linked List |
Medium |
LinkedList |
| 225 |
Implement Stack using Queues |
Easy |
Queue |
| 232 |
Implement Queue using Stacks |
Easy |
Stack |
| 235 |
Lowest Common Ancestor of a Binary Search Tree |
Easy |
Tree |
| 236 |
Lowest Common Ancestor of a Binary Tree |
Medium |
Tree |
| 239 |
Sliding Window Maximum |
Hard |
Queue |
| 242 |
Valid Anagram |
Easy |
HashMap |
| 703 |
Kth Largest Element in a Stream |
Medium |
Stack |
| 938 |
Range Sum of BST |
Easy |
Tree, recursion |
| 1438 |
Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit |
Medium |
Slide window+Monotonic stack |