LeetCode Question Difficulty Distribution

 

             
  ID Question Diff Freq Data Structure Algorithms  
               
             
  1 Two Sum 2 5 array sort
          set Two Pointers
  2 Add Two Numbers 3 4 linked list Two Pointers
            Math
  3 Longest Substring Without Repeating Characters 3 2 string Two Pointers
          hashtable  
  4 Median of Two Sorted Arrays 5 3 array Binary Search
  5 Longest Palindromic Substring 4 2 string  
  6 ZigZag Conversion 3 1 string  
  7 Reverse Integer 2 3   Math
  8 String to Integer (atoi) 2 5 string Math
  9 Palindrome Number 2 2   Math
  10 Regular Expression Matching 5 3 string Recursion
            DP
  11 Container With Most Water 3 2 array Two Pointers
  12 Integer to Roman 3 4   Math
  13 Roman to Integer 2 4   Math
  14 Longest Common Prefix 2 1 string  
  15 3Sum 3 5 array Two Pointers
  16 3Sum Closest 3 1 array Two Pointers
  17 Letter Combinations of a Phone Number 3 3 string DFS
  18 4Sum 3 2 array  
  19 Remove Nth Node From End of List 2 3 linked list Two Pointers
  20 Valid Parentheses 2 5 string Stack
  21 Merge Two Sorted Lists 2 5 linked list sort
            Two Pointers
            merge
  22 Generate Parentheses 3 4 string DFS
  23 Merge k Sorted Lists 3 4 linked list sort
          heap Two Pointers
            merge
  24 Swap Nodes in Pairs 2 4 linked list  
  25 Reverse Nodes in k-Group 4 2 linked list Recursion
            Two Pointers
  26 Remove Duplicates from Sorted Array 1 3 array Two Pointers
  27 Remove Element 1 4 array Two Pointers
  28 Implement strStr() 4 5 string Two Pointers
            KMP
            rolling hash
  29 Divide Two Integers 4 3   Binary Search
            Math
  30 Substring with Concatenation of All Words 3 1 string Two Pointers
  31 Next Permutation 5 2 array permutation
  32 Longest Valid Parentheses 4 1 string DP
  33 Search in Rotated Sorted Array 4 3 array Binary Search
  34 Search for a Range 4 3 array Binary Search
  35 Search Insert Position 2 2 array  
  36 Valid Sudoku 2 2 array  
  37 Sudoku Solver 4 2 array DFS
  38 Count and Say 2 2 string Two Pointers
  39 Combination Sum 3 3 array combination
  40 Combination Sum II 4 2 array combination
  41 First Missing Positive 5 2 array sort
  42 Trapping Rain Water 4 2 array Two Pointers
            Stack
  43 Multiply Strings 4 3 string Two Pointers
            Math
  44 Wildcard Matching 5 3 string Recursion
            DP
            greedy
  45 Jump Game II 4 2 array  
  46 Permutations 3 4 array permutation
  47 Permutations II 4 2 array permutation
  48 Rotate Image 4 2 array  
  49 Anagrams 3 4 string  
          hashtable  
  50 Pow(x, n) 3 5   Binary Search
            Math
  51 N-Queens 4 3 array DFS
  52 N-Queens II 4 3 array DFS
  53 Maximum Subarray 3 3 array DP
  54 Spiral Matrix 4 2 array  
  55 Jump Game 3 2 array  
  56 Merge Intervals 4 5 array sort
          linked list merge
          red-black tree  
  57 Insert Interval 4 5 array sort
          linked list merge
          red-black tree  
  58 Length of Last Word 1 1 string  
  59 Spiral Matrix II 3 2 array  
  60 Permutation Sequence 5 1   permutation
            Math
  61 Rotate List 3 2 linked list Two Pointers
  62 Unique Paths 2 3 array DP
  63 Unique Paths II 3 3 array DP
  64 Minimum Path Sum 3 3 array DP
  65 Valid Number 2 5 string Math
  66 Plus One 1 2 array Math
  67 Add Binary 2 4 string Two Pointers
            Math
  68 Text Justification 4 2 string  
  69 Sqrt(x) 4 4   Binary Search
  70 Climbing Stairs 2 5   DP
  71 Simplify Path 3 1 string Stack
  72 Edit Distance 4 3 string DP
  73 Set Matrix Zeroes 3 5 array  
  74 Search a 2D Matrix 3 3 array Binary Search
  75 Sort Colors 4 2 array sort
            Two Pointers
  76 Minimum Window Substring 4 2 string Two Pointers
  77 Combinations 3 4   combination
  78 Subsets 3 4 array Recursion
            combination
  79 Word Search 3 4 array DFS
  80 Remove Duplicates from Sorted Array II 2 2 array Two Pointers
  81 Search in Rotated Sorted Array II 5 3 array Binary Search
  82 Remove Duplicates from Sorted List II 3 3 linked list Recursion
            Two Pointers
  83 Remove Duplicates from Sorted List 1 3 linked list  
  84 Largest Rectangle in Histogram 5 2 array Stack
  85 Maximal Rectangle 5 1 array DP
            Stack
  86 Partition List 3 3 linked list Two Pointers
  87 Scramble String 5 2 string Recursion
            DP
  88 Merge Sorted Array 2 5 array Two Pointers
            merge
  89 Gray Code 4 2   combination
  90 Subsets II 4 2 array Recursion
            combination
  91 Decode Ways 3 4 string Recursion
            DP
  92 Reverse Linked List II 3 2 linked list Two Pointers
  93 Restore IP Addresses 3 3 string DFS
  94 Binary Tree Inorder Traversal 4 3 tree Recursion
          hashtable morris
            Stack
  95 Unique Binary Search Trees II 4 1 tree DP
            DFS
  96 Unique Binary Search Trees 3 1 tree DP
  97 Interleaving String 5 2 string Recursion
            DP
  98 Validate Binary Search Tree 3 5 tree DFS
  99 Recover Binary Search Tree 4 2 tree DFS
  100 Same Tree 1 1 tree DFS
  101 Symmetric Tree 1 2 tree DFS
  102 Binary Tree Level Order Traversal 3 4 tree BFS
  103 Binary Tree Zigzag Level Order Traversal 4 3 queue BFS
          tree Stack
  104 Maximum Depth of Binary Tree 1 1 tree DFS
  105 Construct Binary Tree from Preorder and Inorder Tr 3 3 array DFS
          tree  
  106 Construct Binary Tree from Inorder and Postorder T 3 3 array DFS
          tree  
  107 Binary Tree Level Order Traversal II 3 1 tree BFS
  108 Convert Sorted Array to Binary Search Tree 2 3 tree DFS
  109 Convert Sorted List to Binary Search Tree 4 3 linked list Recursion
            Two Pointers
  110 Balanced Binary Tree 1 2 tree DFS
  111 Minimum Depth of Binary Tree 1 1 tree DFS
  112 Path Sum 1 3 tree DFS
  113 Path Sum II 2 2 tree DFS
  114 Flatten Binary Tree to Linked List 3 3 tree Recursion
            Stack
  115 Distinct Subsequences 4 2 string DP
  116 Populating Next Right Pointers in Each Node 3 3 tree DFS
  117 Populating Next Right Pointers in Each Node II 4 2 tree DFS
  118 Pascal's Triangle 2 1 array  
  119 Pascal's Triangle II 2 1 array  
  120 Triangle 3 1 array DP
  121 Best Time to Buy and Sell Stock 2 1 array DP
  122 Best Time to Buy and Sell Stock II 3 1 array greedy
  123 Best Time to Buy and Sell Stock III 4 1 array DP
  124 Binary Tree Maximum Path Sum 4 2 tree DFS
  125 Valid Palindrome 2 5 string Two Pointers
  126 Word Ladder II 1 1    
  127 Word Ladder 3 5 graph BFS
            shortest path
  128 Longest Consecutive Sequence 4 3 array  
  129 Sum Root to Leaf Numbers 2 4 tree DFS
  130 Surrounded Regions 4 3 array BFS
            DFS
  131 Palindrome Partitioning 3 4 string DFS
  132 Palindrome Partitioning II 4 3 string DP

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