"100 Must-Do LeetCode Problems: A Comprehensive Guide to Data Structures and Algorithms Practice"

 

Arrays

1. Two Sum: Given an array of integers, return indices of the two numbers such that they add up to a specific target.
2. Best Time to Buy and Sell Stock: Find the maximum profit you can achieve from buying and selling stocks.
3. Contains Duplicate: Determine if any value appears at least twice in the array.
4. Product of Array Except Self: Return an array where each element is the product of all elements except itself.
5. Maximum Subarray: Find the contiguous subarray with the largest sum.
6. Move Zeroes: Move all zeroes in an array to the end while maintaining the relative order of non-zero elements.
7. Merge Intervals: Given a collection of intervals, merge all overlapping intervals.
8. 3Sum: Find all unique triplets in an array that sum up to zero.
9. Maximum Product Subarray: Find the contiguous subarray within an array that has the largest product.
10. Find Minimum in Rotated Sorted Array: Given a rotated sorted array, find the minimum element.

Strings

11. Longest Substring Without Repeating Characters: Find the length of the longest substring without repeating characters.
12. Valid Anagram: Determine if two strings are anagrams of each other.
13. Group Anagrams: Group an array of strings into anagrams.
14. Longest Palindromic Substring: Find the longest palindromic substring in a string.
15. String to Integer (atoi): Implement a function to convert a string to an integer.
16. Implement strStr(): Locate a substring within a string.
17. Count and Say: Generate the n-th term of the "count and say" sequence.
18. Reverse String: Reverse a string in-place.
19. Valid Parentheses: Determine if the input string’s parentheses are valid.
20. Generate Parentheses: Generate all combinations of well-formed parentheses.

Linked Lists

21. Reverse Linked List: Reverse a singly linked list.
22. Merge Two Sorted Lists: Merge two sorted linked lists into one sorted list.
23. Linked List Cycle: Detect if a linked list has a cycle.
24. Remove Nth Node From End of List: Remove the n-th node from the end of a linked list.
25. Palindrome Linked List: Determine if a linked list is a palindrome.
26. Intersection of Two Linked Lists: Find the node where two linked lists intersect.
27. Add Two Numbers: Add two numbers represented by linked lists.
28. Swap Nodes in Pairs: Swap every two adjacent nodes in a linked list.
29. Reorder List: Reorder a linked list so that nodes are in a specific sequence.
30. LRU Cache: Design a data structure that follows the constraints of a Least Recently Used (LRU) cache.

Trees

31. Maximum Depth of Binary Tree: Find the maximum depth of a binary tree.
32. Invert Binary Tree: Invert a binary tree.
33. Validate Binary Search Tree: Check if a binary tree is a valid binary search tree.
34. Symmetric Tree: Determine if a binary tree is symmetric.
35. Binary Tree Level Order Traversal: Return the level order traversal of a binary tree’s nodes' values.
36. Lowest Common Ancestor of a Binary Tree: Find the lowest common ancestor of two nodes in a binary tree.
37. Serialize and Deserialize Binary Tree: Design an algorithm to serialize and deserialize a binary tree.
38. Binary Tree Inorder Traversal: Perform an inorder traversal of a binary tree.
39. Kth Smallest Element in a BST: Find the k-th smallest element in a binary search tree.
40. Construct Binary Tree from Preorder and Inorder Traversal: Construct a binary tree from its preorder and inorder traversal.

Graphs

41. Number of Islands: Count the number of islands in a 2D grid.
42. Clone Graph: Clone an undirected graph.
43. Course Schedule: Determine if you can finish all courses given prerequisites.
44. Graph Valid Tree: Check if a graph is a valid tree.
45. Pacific Atlantic Water Flow: Find all cells in a matrix where water can flow to both the Pacific and Atlantic oceans.
46. Rotting Oranges: Given a grid of oranges, determine how long it takes for all oranges to rot.
47. Word Ladder: Transform one word into another by changing one letter at a time.
48. Minimum Height Trees: Find the root nodes of minimum height trees in an undirected graph.
49. Max Area of Island: Find the maximum area of an island in a grid.
50. Cheapest Flights Within K Stops: Find the cheapest price to travel from one city to another with at most K stops.

Dynamic Programming

51. Climbing Stairs: Find the number of distinct ways to climb to the top of a staircase.
52. Coin Change: Determine the minimum number of coins needed to make a certain amount.
53. Longest Increasing Subsequence: Find the length of the longest increasing subsequence.
54. House Robber: Maximize the amount of money you can rob without robbing adjacent houses.
55. Unique Paths: Calculate how many unique paths exist in a grid from the top-left to the bottom-right corner.
56. Edit Distance: Find the minimum number of operations required to convert one string into another.
57. Maximum Product Subarray: Similar to earlier, but focused on products instead of sums.
58. Decode Ways: Count the number of ways to decode a string.
59. Jump Game: Determine if you can reach the last index of the array from the first index.
60. Partition Equal Subset Sum: Determine if a set can be partitioned into two subsets with equal sums.

Backtracking

61. Permutations: Generate all possible permutations of a list of numbers.
62. Subsets: Find all possible subsets of a set.
63. Combination Sum: Find all unique combinations that sum to a target.
64. N-Queens: Solve the N-Queens puzzle.
65. Word Search: Determine if a word exists in a 2D board.
66. Combination Sum II: Similar to Combination Sum but with duplicates allowed.
67. Palindrome Partitioning: Partition a string into palindromic substrings.
68. Generate Parentheses: Generate all combinations of well-formed parentheses.
69. Letter Combinations of a Phone Number: Generate all possible letter combinations from a phone number.
70. Solve Sudoku: Implement a function to solve a Sudoku puzzle.

Miscellaneous

71. Minimum Window Substring: Find the minimum window in a string that contains all characters of another string.
72. Find First and Last Position of Element in Sorted Array: Find the starting and ending position of a given target value.
73. Kth Largest Element in an Array: Find the k-th largest element in an unsorted array.
74. Longest Repeating Character Replacement: Find the length of the longest substring with repeating characters.
75. Sliding Window Maximum: Find the maximum in every sliding window of size k.
76. Sum of Two Integers: Implement addition without using operators.
77. Number of Ways to Paint N × 3 Grid: Count the number of ways to paint a grid with certain conditions.
78. Binary Number with Alternating Bits: Check if a number has alternating bits.
79. Maximum Length of Repeated Subarray: Find the maximum length of a subarray that appears in both arrays.
80. Find All Anagrams in a String: Find all start indices of anagrams of a string in another string.

Advanced

81. Design Search Autocomplete System: Create a system that suggests completions for user input.
82. Maximal Rectangle: Find the largest rectangle containing only 1s in a binary matrix.
83. Russian Doll Envelopes: Find the maximum number of envelopes you can Russian doll.
84. Sliding Puzzle: Solve the sliding puzzle game.
85. Top K Frequent Elements: Find the k most frequent elements in an array.
86. Number of Subarrays with Sum K: Count the number of contiguous subarrays that sum to a given k.
87. Longest Substring with At Most K Distinct Characters: Find the length of the longest substring with at most k distinct characters.
88. Alien Dictionary: Determine the order of characters in an alien language.
89. Task Scheduler: Find the least number of intervals needed to complete all tasks given cooldowns.
90. Find Minimum in Rotated Sorted Array II: Find the minimum in a rotated sorted array that may contain duplicates.

Interview-Style Problems

91. Binary Tree Maximum Path Sum: Find the maximum path sum in a binary tree.
92. Search in Rotated Sorted Array: Search for a target in a rotated sorted array.
93. Count of Smaller Numbers After Self: Count the number of smaller elements to the right of each element.
94. Design an Excel Sheet: Implement a system to represent an Excel sheet.
95. Word Break: Determine if a string can be segmented into words from a dictionary.
96. Maximum Product of Three Numbers: Find the maximum product of any three numbers in an array.
97. Delete Node in a Linked List: Delete a node (except the tail) from a linked list.
98. Count Vowels Permutation: Count the number of valid strings that can be formed from a set of vowels.
99. Subarray Sum Equals K: Count the number of continuous subarrays that sum to k.
100. Rotate Array: Rotate an array to the right by k steps.