1 Trapping Rain Water Array Two Pointers Dynamic Programming Stack Monotonic Stack
Hard 100
0.7% 2 Merge Intervals Array Sorting
Medium 100
0.5% 3 LRU Cache Hash Table Linked List Design Doubly-Linked List
Medium 100
0.5% 4 Flatten Nested List Iterator Stack Tree Depth-First Search Design Queue Iterator
Medium 100
0.7% 5 Tweet Counts Per Frequency Hash Table String Binary Search Design Sorting Ordered Set
Medium 100
0.5% 6 Regular Expression Matching String Dynamic Programming Recursion
Hard 97
0.3% 7 Integer to Roman Hash Table Math String
Medium 97
0.7% 8 Valid Parentheses String Stack
Easy 97
0.4% 9 Merge k Sorted Lists Linked List Divide and Conquer Heap (Priority Queue) Merge Sort
Hard 97
0.6% 10 Multiply Strings Math String Simulation
Medium 97
0.4% 11 Wildcard Matching String Dynamic Programming Greedy Recursion
Hard 97
0.3% 12 Permutation Sequence Math Recursion
Hard 97
0.5% 13 Pascal's Triangle Array Dynamic Programming
Easy 97
0.8% 14 Word Break II Array Hash Table String Dynamic Programming Backtracking Trie Memoization
Hard 97
0.6% 15 Time Needed to Buy Tickets Array Queue Simulation
Easy 97
0.7% 16 Max Points on a Line Array Hash Table Math Geometry
Hard 97
0.3% 17 One Edit Distance Two Pointers String
Medium 97
0.3% 18 Happy Number Hash Table Math Two Pointers
Easy 97
0.6% 19 Reverse Linked List Linked List Recursion
Easy 97
0.8% 20 Implement Trie (Prefix Tree) Hash Table String Design Trie
Medium 97
0.7% 21 The Skyline Problem Array Divide and Conquer Binary Indexed Tree Segment Tree Sweep Line Sorting Heap (Priority Queue) Ordered Set
Hard 97
0.5% 22 Lowest Common Ancestor of a Binary Search Tree Tree Depth-First Search Binary Search Tree Binary Tree
Medium 97
0.7% 23 Flatten 2D Vector Array Two Pointers Design Iterator
Medium 97
0.5% 24 Alien Dictionary Array String Depth-First Search Breadth-First Search Graph Theory Topological Sort
Hard 97
0.4% 25 Best Meeting Point Array Math Sorting Matrix
Hard 97
0.6% 26 Design Skiplist Linked List Design
Hard 97
0.6% 27 Number of Connected Components in an Undirected Graph Depth-First Search Breadth-First Search Union-Find Graph Theory
Medium 97
0.7% 28 Design Twitter Hash Table Linked List Design Heap (Priority Queue)
Medium 97
0.4% 29 Kth Smallest Element in a Sorted Matrix Array Binary Search Sorting Heap (Priority Queue) Matrix
Medium 97
0.6% 30 Insert Delete GetRandom O(1) Array Hash Table Math Design Randomized
Medium 97
0.6% 31 Trapping Rain Water II Array Breadth-First Search Heap (Priority Queue) Matrix
Hard 97
0.6% 32 Minimum Genetic Mutation Hash Table String Breadth-First Search
Medium 97
0.6% 33 Minimum Number of Steps to Make Two Strings Anagram Hash Table String Counting
Medium 97
0.8% 34 Validate IP Address String
Medium 97
0.3% 35 Count Student Number in Departments Database
Medium 97
0.6% 36 Rectangles Area Database
Medium 97
0.7% 37 Investments in 2016 Database
Medium 97
0.5% 38 Customer Placing the Largest Number of Orders Database
Easy 97
0.6% 39 Tree Node Database
Medium 97
0.8% 40 Invalid Tweets Database
Easy 97
0.9% 41 Number of Black Blocks Array Hash Table Enumeration
Medium 97
0.4% 42 Masking Personal Information String
Medium 97
0.6% 43 Design Authentication Manager Hash Table Linked List Design Doubly-Linked List
Medium 97
0.6% 44 Minimum Elements to Add to Form a Given Sum Array Greedy
Medium 97
0.5% 45 Binary Gap Bit Manipulation
Easy 97
0.7% 46 Finding the Users Active Minutes Array Hash Table
Medium 97
0.8% 47 Process Tasks Using Servers Array Heap (Priority Queue)
Medium 97
0.4% 48 Remove All Occurrences of a Substring String Stack Simulation
Medium 97
0.8% 49 Count Sub Islands Array Depth-First Search Breadth-First Search Union-Find Matrix
Medium 97
0.7% 50 Largest Plus Sign Array Dynamic Programming
Medium 63
0.5% 51 Minimum Cost to Connect Sticks Array Greedy Heap (Priority Queue)
Medium 52
0.7%