LeetCode LeetCode Algorithm # Title Solution Difficulty 1 Two Sum go Easy 2 Add Two Numbers go Medium 3 Longest Substring Without Repeating Characters go Medium 4 Median of Two Sorted Arrays go Hard 5 Longest Palindromic Substring go Medium 6 ZigZag Conversion go Easy 7 Reverse Integer go Easy 8 String to Integer (atoi) go Easy 9 Palindrome Number go Easy 10 Regular Expression Matching go Hard 11 Container With Most Water go Medium 12 Integer to Roman go Medium 13 Roman to Integer go Easy 14 Longest Common Prefix go Easy 15 3Sum go Medium 16 3Sum Closest go Medium 17 Letter Combinations of a Phone Number go Medium 18 4Sum go Medium 19 Remove Nth Node From End of List go Easy 20 Valid Parentheses go Easy 21 Merge Two Sorted Lists go Easy 22 Generate Parentheses go Medium 23 Merge k Sorted Lists go Hard 24 Swap Nodes in Pairs go Medium 25 Reverse Nodes in k-Group go Hard 26 Remove Duplicates from Sorted Array Easy 27 Remove Element Easy 28 Implement strStr() Easy 29 Divide Two Integers Medium 30 Substring with Concatenation of All Words Hard 31 Next Permutation Medium 32 Longest Valid Parentheses Hard 33 Search in Rotated Sorted Array go Hard 34 Search for a Range Medium 35 Search Insert Position Medium 36 Valid Sudoku Easy 37 Sudoku Solver Hard 38 Count and Say Easy 39 Combination Sum Medium 40 Combination Sum II Medium 41 First Missing Positive Hard 42 Trapping Rain Water Hard 43 Multiply Strings Medium 44 Wildcard Matching Hard 45 Jump Game II Hard 46 Permutations Medium 47 Permutations II Hard 48 Rotate Image Medium 49 Group Anagrams Medium 50 Pow(x, n) Medium