Top Interview Questions # Problems Difficulty Solution 001 Two_Sum Easy Java 002 Add Two Numbers Medium Java 003 Longest Substring Without Repeating Characters Medium Java 004 Median of Two Sorted Arrays Hard Java 005 Longest Palindromic Substring Medium Java 007 Reverse Integer Easy Java 008 String to Integer (atoi) Medium Java 010 Regular Expression Matching Hard Java 011 Container With Most Water Medium Java 013 Roman to Integer Easy Java 014 Longest Common Prefix Easy Java 015 3Sum Medium Java 017 Letter Combinations of a Phone Number Medium Java 019 Remove Nth Node From End of List Easy Java 020 Valid Parentheses Easy Java 021 Merge Two Sorted Lists Easy Java 022 Generate Parentheses Medium Java 023 Merge k Sorted Lists Hard Java 026 Remove Duplicates from Sorted Array Easy Java 028 Implement strStr() Easy Java 029 Divide Two Integers Medium Java 033 Search in Rotated Sorted Array Medium Java 034 Search for a Range Medium Java 035 Search Insert Position Medium Java 036 Valid Sudoku Medium Java 038 Count and Say Easy Java 041 First Missing Positive Hard Java 042 Trapping Rain Water Hard Java 044 Wildcard Matching Hard Java 046 Permutations Medium Java 048 Rotate Image Medium Java 049 Group Anagrams Medium Java 050 Pow(x, n) Medium Java 053 Maximum Subarray Medium Java 054 Spiral Matrix Medium Java 055 Jump Game Medium Java 056 Merge Intervals Medium Java 062 Unique Paths Medium Java 066 Plus One Easy Java 069 Sqrt(x) Easy Java 070 Climbing Stairs Easy Java 073 Set Matrix Zeroes Medium Java 075 Sort Colors Medium Java 076 Minimum Window Substring Hard Java 078 Subsets Medium Java 079 Word Search Medium Java 084 Largest Rectangle in Histogram Hard Java 088 Merge Sorted Array Easy Java 091 Decode Ways Medium Java 094 Binary Tree Inorder Traversal Medium Java 098 Validate Binary Search Tree Medium Java 101 Symmetric Tree Easy Java 102 Binary Tree Level Order Traversal Easy Java 103 Binary Tree Zigzag Level Order Traversal Medium Java 104 Maximum Depth of Binary Tree Easy Java 105 Construct Binary Tree from Preorder and Inorder Traversal Medium Java 108 Convert Sorted Array to Binary Search Tree Easy Java 116 Populating Next Right Pointers in Each Node Medium Java 118 Pascal's Triangle Easy Java 121 Best Time to Buy and Sell Stock Easy Java 122 Best Time to Buy and Sell Stock II Easy Java 124 Binary Tree Maximum Path Sum Hard Java 125 Valid Palindrome Easy Java 127 Word Ladder Medium Java 128 Longest Consecutive Sequence Hard Java 130 Surrounded Regions Medium Java 131 Palindrome Partitioning Medium Java 134 Gas Station Medium Java 136 Single Number Easy Java 138 Copy List with Random Pointer Medium Java 139 Word Break Medium Java 140 Word Break II Hard Java 141 Linked List Cycle Easy Java 146 LRU Cache Hard Java 148 Sort List Medium Java 149 Max Points on a Line Hard Java 150 Evaluate Reverse Polish Notation Medium Java 152 Maximum Product Subarray Medium Java 155 Min Stack Easy Java 160 Intersection of Two Linked Lists Easy Java 162 Find Peak Element Medium Java 163 Missing Ranges Medium [没权限] 166 Fraction to Recurring Decimal Medium Java 169 Majority Element Easy Java 171 Excel Sheet Column Number Easy Java 172 Factorial Trailing Zeroes Easy Java 179 Largest Number Medium Java 189 Rotate Array Easy Java 190 Reverse Bits Easy Java 191 Number of 1 Bits Easy Java 198 House Robber Easy Java 200 Number of Islands Medium Java 202 Happy Number Easy Java 204 Count Primes Easy Java 206 Reverse Linked List Easy Java 207 Course Schedule Medium Java 208 Implement Trie (Prefix Tree) Medium Java 210 Course Schedule II Medium Java 212 Word Search II Hard Java 215 Kth Largest Element in an Array Medium Java 217 Contains Duplicate Easy Java 218 The Skyline Problem Hard Java 227 Basic Calculator II Medium Java 230 Kth Smallest Element in a BST Medium Java 234 Palindrome Linked List Easy Java 236 Lowest Common Ancestor of a Binary Tree Medium Java 237 Delete Node in a Linked List Easy Java 238 Product of Array Except Self Medium Java 239 Sliding Window Maximum Hard Java 240 Search a 2D Matrix II Medium Java 242 Valid Anagram Easy Java 251 Flatten 2D Vector Medium [没权限] 253 Meeting Rooms II Medium [没权限] 268 Missing Number Easy Java 269 Alien Dictionary Hard [没权限] 277 Find the Celebrity Medium [没权限] 279 Perfect Squares Medium Java 283 Move Zeroes Easy Java 285 Inorder Successor in BST Medium [没权限] 287 Find the Duplicate Number Hard Java 295 Find Median from Data Stream Hard Java 297 Serialize and Deserialize Binary Tree Hard Java 300 Longest Increasing Subsequence Medium Java 308 Range Sum Query 2D - Mutable Medium [没权限] 315 Count of Smaller Numbers After Self Hard Java 322 Coin Change Medium Java 324 Wiggle Sort II Medium Java 326 Power of Three Easy Java 328 Odd Even Linked List Medium Java 329 Longest Increasing Path in a Matrix Hard Java 334 Increasing Triplet Subsequence Medium Java 340 Longest Substring with At Most K Distinct Characters Hard Java 341 Flatten Nested List Iterator Medium Java 344 Reverse String Easy Java 347 Top K Frequent Elements Medium Java 348 Design Tic-Tac-Toe Medium [没权限] 350 Intersection of Two Arrays II Easy Java 371 Sum of Two Integers Easy Java 378 Kth Smallest Element in a Sorted Matrix Medium Java 380 Insert Delete GetRandom O(1) Medium Java 384 Shuffle an Array Medium Java 387 First Unique Character in a String Easy Java 395 Longest Substring with At Least K Repeating Characters Medium Java 412 Fizz Buzz Easy Java 454 4Sum II Medium Java