leetcode Leetcode Problem Solutions # Title Solution Difficulty 1 Two Sum Java Easy 4 Median of Two Sorted Arrays Java Hard 5 Longest Palindromic Substring Java Medium 6 ZigZag Conversion Java Medium 7 Reverse Integer Java Easy 9 Palindrome Number Java Easy 10 Regular Expression Matching Java Hard 11 Container With Most Water Java Medium 12 Integer to Roman Java Medium 13 Roman to Integer Java Easy 15 3Sum Java Medium 16 3Sum Closest Java Medium 17 Letter Combinations of a Phone Number Java Medium 18 4Sum Java Medium 20 Valid Parentheses Java Easy 21 Merge Two Sorted Lists Java Easy 48 Rotate Image Java Medium 56 Merge Intervals Java Medium 59 Spiral Matrix II Java Medium 75 Sort Colors Java Medium 119 Pascal's Triangle II Java Easy 136 Single Number Java Easy 169 Majority Element Java Easy 238 Product of Array Except Self Java Medium 240 Search a 2D Matrix II Java Medium 290 Word Pattern Java Easy 334 Increasing Triplet Subsequence Java Medium 409 Longest Palindrome Java Easy 415 Add Strings Java Easy 560 Subarray Sum Equals K Java Medium 706 Design HashMap Java Easy 733 Flood Fill Java Easy 946 Validate Stack Sequences Java Medium