1 Number of Islands Array Depth-First Search Breadth-First Search Union-Find Matrix
Medium 100
0.6% 2 Merge Intervals Array Sorting
Medium 94
0.5% 3 Container With Most Water Array Two Pointers Greedy
Medium 92
0.6% 4 Integer to Roman Hash Table Math String
Medium 92
0.7% 5 Add Two Numbers Linked List Math Recursion
Medium 90
0.5% 6 Longest Palindromic Substring Two Pointers String Dynamic Programming
Medium 90
0.4% 7 Alien Dictionary Array String Depth-First Search Breadth-First Search Graph Theory Topological Sort
Hard 90
0.4% 8 3Sum Array Two Pointers Sorting
Medium 90
0.4% 9 Merge Two Sorted Lists Linked List Recursion
Easy 90
0.7% 10 Move Zeroes Array Two Pointers
Easy 90
0.6% 11 Diameter of Binary Tree Tree Depth-First Search Binary Tree
Easy 90
0.7% 12 Minimum Distance Between BST Nodes Tree Depth-First Search Breadth-First Search Binary Search Tree Binary Tree
Easy 90
0.6% 13 Trapping Rain Water Array Two Pointers Dynamic Programming Stack Monotonic Stack
Hard 90
0.7% 14 Design HashSet Array Hash Table Linked List Design Hash Function
Easy 90
0.7% 15 Pow(x, n) Math Recursion
Medium 90
0.4% 16 Maximum Subarray Array Divide and Conquer Dynamic Programming
Medium 90
0.5% 17 Unique Morse Code Words Array Hash Table String
Easy 90
0.8% 18 Subdomain Visit Count Array Hash Table String Counting
Medium 90
0.8% 19 Palindrome Pairs Array Hash Table String Trie Hash Function
Hard 90
0.4% 20 Power of Four Math Bit Manipulation Recursion
Easy 90
0.5% 21 Intersection of Two Arrays Array Hash Table Two Pointers Binary Search Sorting
Easy 90
0.8% 22 Validate Binary Search Tree Tree Depth-First Search Binary Search Tree Binary Tree
Medium 90
0.4% 23 Longest String Chain Array Hash Table Two Pointers String Dynamic Programming Sorting
Medium 90
0.6% 24 Search Suggestions System Array String Binary Search Trie Sorting Heap (Priority Queue)
Medium 90
0.7% 25 Binary Tree Maximum Path Sum Dynamic Programming Tree Depth-First Search Binary Tree
Hard 90
0.4% 26 All Nodes Distance K in Binary Tree Hash Table Tree Depth-First Search Breadth-First Search Binary Tree
Medium 90
0.7% 27 Clone Graph Hash Table Depth-First Search Breadth-First Search Graph Theory
Medium 90
0.7% 28 Is Subsequence Two Pointers String Dynamic Programming
Easy 90
0.5% 29 Copy List with Random Pointer Hash Table Linked List
Medium 90
0.6% 30 Employees Earning More Than Their Managers Database
Easy 90
0.7% 31 Unique Email Addresses Array Hash Table String
Easy 90
0.7% 32 Binary Tree Right Side View Tree Depth-First Search Breadth-First Search Binary Tree
Medium 90
0.7% 33 Verifying an Alien Dictionary Array Hash Table String
Easy 90
0.6% 34 Lowest Common Ancestor of a Binary Tree Tree Depth-First Search Binary Tree
Medium 90
0.7% 35 Shortest Word Distance Array String
Easy 90
0.7% 36 K Closest Points to Origin Array Math Divide and Conquer Geometry Sorting Heap (Priority Queue) Quickselect
Medium 90
0.7% 37 Invalid Transactions Array Hash Table String Sorting
Medium 90
0.3% 38 Group Shifted Strings Array Hash Table String
Medium 90
0.7% 39 Rotting Oranges Array Breadth-First Search Matrix
Medium 87
0.6% 40 Strong Password Checker String Greedy Heap (Priority Queue)
Hard 84
0.2% 41 Decode String String Stack Recursion
Medium 80
0.6% 42 Roman to Integer Hash Table Math String
Easy 76
0.7% 43 Median of Two Sorted Arrays Array Binary Search Divide and Conquer
Hard 72
0.5% 44 Word Search II Array String Backtracking Trie Matrix
Hard 72
0.4% 45 Subsets Array Backtracking Bit Manipulation
Medium 66
0.8% 46 Escape The Ghosts Array Math
Medium 66
0.6% 47 As Far from Land as Possible Array Dynamic Programming Breadth-First Search Matrix
Medium 66
0.5% 48 Reconstruct Original Digits from English Hash Table Math String
Medium 48
0.5% 49 Word Search Array String Backtracking Depth-First Search Matrix
Medium 48
0.5% 50 Find Peak Element Array Binary Search
Medium 48
0.5% 51 Count and Say String
Medium 48
0.6% 52 Valid Parentheses String Stack
Easy 48
0.4% 53 Lowest Common Ancestor of a Binary Tree III Hash Table Two Pointers Tree Binary Tree
Medium 48
0.8% 54 Shortest Distance from All Buildings Array Breadth-First Search Matrix
Hard 48
0.4% 55 Fibonacci Number Math Dynamic Programming Recursion Memoization
Easy 48
0.7%