100 Days of LeetCode

completed 2025-10-19 2026-02-08 5 min read 837 words

100 LeetCode problems across arrays, trees, graphs, DP, sliding window & more.

repo → Coding-Interview-Preparation

Problem Solution Preview Level / Approach (Language)
1. Two Sum Python Solution Easy / Array (Python)
2. Concatenation of Array Python Solution Easy / Array (Python)
3. Reverse String Python Solution Easy / String Manipulation (Python)
4. Contains Duplicate C++ Solution Easy / Hash Table (C++)
5. Valid Palindrome Python Solution Easy / Two Pointers (Python)
6. Best Time to Buy and Sell Stock Python Solution Easy / Dynamic Programming (Python)
7. Valid Parentheses Python Solution Easy / Stack (Python)
8. Binary Search Python Solution Easy / Binary Search (Python)
9. Reverse Linked List Python Solution Easy / Linked List (Python)
10. Invert Binary Tree Python Solution Easy / Binary Tree (Python)
11. Top K Frequent Elements Python Solution Medium / Heap/Hash Table (Python)
12. Two Sum II - Input Array Is Sorted Python Solution Medium / Binary Search (Python)
13. Longest Substring Without Repeating Characters Python Solution Medium / Sliding Window (Python)
14. Min Stack Solution Medium / Stack (Python)
15. Evaluate Reverse Polish Notation Solution Medium / Stack (Python)
16. Search a 2D Matrix Solution Medium / Binary Search (Python)
17. Reorder List Solution Medium / Linked List (Python)
18. Lowest Common Ancestor of a Binary Search Tree Solution Medium / Binary Search Tree (Python)
19. Subsets Solution Medium / Backtracking (Python)
20. K Closest Points to Origin Solution Medium / Heap/Sorting (Python)
21. Number of Islands Solution Medium / DFS (Python)
22. Sum of Two Integers Solution Medium / Bit Manipulation (Python)
23. Maximum Subarray Solution Medium / Kadane’s Algorithm (Python)
24. Insert Interval Solution Medium / Greedy (Python)
25. Rotate Image Solution Medium / Matrix Manipulation (Python)
26. Climbing Stairs Solution Easy / Dynamic Programming (Python)
27. Unique Paths Solution Medium / Dynamic Programming (Python)
28. Min Cost Climbing Stairs Solution Easy / Dynamic Programming (Python)
29. Longest Common Subsequence Solution Medium / Dynamic Programming (Python)
30. House Robber Solution Medium / Dynamic Programming (Python)
31. Best Time to Buy and Sell Stock with Cooldown Solution Medium / Dynamic Programming (Python)
32. Max Area of Island Solution Medium / DFS (Python)
33. Last Stone Weight Solution Easy / Heap (Python)
34. Kth Largest Element in an Array Solution Medium / Heap/Quickselect (Python)
35. Combination Sum Solution Medium / Backtracking (Python)
36. Combination Sum II Solution Medium / Backtracking (Python)
37. Jump Game Solution Medium / Greedy (Python)
38. Jump Game II Solution Hard / Greedy (Python)
39. 3Sum Solution Medium / Two Pointers (Python)
40. Koko Eating Bananas Solution Medium / Binary Search (Python)
41. Merge Two Sorted Lists Solution Easy / Linked List (Python)
42. Linked List Cycle Solution Easy / Linked List (Python)
43. Binary Tree Level Order Traversal Solution Medium / Binary Tree (Python)
44. Binary Tree Right Side View Solution Medium / Binary Tree (Python)
45. Maximum Depth of Binary Tree Solution Easy / Binary Tree (Python)
46. Valid Sudoku Solution Medium / Hash Table (Python)
47. Longest Repeating Character Replacement Solution Medium / Sliding Window (Python)
48. Daily Temperatures Solution Medium / Stack (Python)
49. Generate Parentheses Solution Medium / Backtracking (Python)
50. Remove Nth Node From End of List Solution Medium / Linked List (Python)
51. Copy List with Random Pointer Solution Medium / Linked List (Python)
52. Permutations Solution Medium / Backtracking (Python)
53. Count Good Nodes in Binary Tree Solution Medium / Binary Tree (Python)
54. Clone Graph Solution Medium / Graph (Python)
55. Rotting Oranges Solution Medium / BFS (Python)
56. House Robber II Solution Medium / Dynamic Programming (Python)
57. Longest Palindromic Substring Solution Medium / Dynamic Programming (Python)
58. Course Schedule Solution Medium / Graph (Python)
59. Gas Station Solution Medium / Greedy (Python)
60. Hand of Straights Solution Medium / Greedy/minHeap (Python)
61. Find Minimum in Rotated Sorted Array Solution Medium / Binary Search (Python)
62. Add Two Numbers Solution Medium / Linked List (Python)
63. Palindromic Substrings Solution Medium / Expand Around Center (Python)
64. Decode Ways Solution Medium / Recursion (Python)
65. Non-overlapping Intervals Solution Medium / Greedy/Sorting (Python)
66. Spiral Matrix Solution Medium / Matrix Traversal (Python)
67. Longest Consecutive Sequence Solution Medium / Hash Set (Python)
68. LRU Cache Solution Medium / Hash Map/Doubly Linked List (Python)
69. Validate Binary Search Tree Solution Medium / Binary Search Tree (Python)
70. Find the Duplicate Number Solution Medium / Floyd’s Cycle Detection (Python)
71. Search in Rotated Sorted Array Solution Medium / Binary Search (Python)
72. Word Search Solution Medium / Backtracking (Python)
73. Container With Most Water Solution Medium / Two Pointers (Python)
74. Trapping Rain Water Solution Hard / Two Pointers (Python)
75. Permutation in String Solution Medium / Sliding Window (Python)
76. Minimum Window Substring Solution Hard / Sliding Window (Python)
77. Sliding Window Maximum Solution Hard / Deque (Python)
78. Car Fleet Solution Medium / Stack (Python)
79. Implement Trie (Prefix Tree) Solution Medium / Trie (Python)
80. Coin Change Solution Medium / Dynamic Programming (Python)
81. Kth Smallest Element in a BST Solution Medium / Binary Search Tree (Python)
82. Construct Binary Tree from Preorder and Inorder Traversal Solution Medium / Binary Tree (Python)
83. Task Scheduler Solution Medium / Counter (Python)
84. Maximum Product Subarray Solution Medium / Dynamic Programming (Python)
85. Regular Expression Matching Solution Hard / Dynamic Programming (Python)
86. N-Queens Solution Hard / Backtracking (Python)
87. Interleaving String Solution Medium / Recursion (Python)
88. Number of 1 Bits Solution Easy / Bit Manipulation (Python)
89. Longest Increasing Subsequence Solution Medium / Dynamic Programming (Python)
90. Surrounded Regions Solution Medium / DFS (Python)
91. Distinct Subsequences Solution Hard / Dynamic Programming (Python)
92. Partition Equal Subset Sum Solution Medium / Dynamic Programming (Python)
93. Design Twitter Solution Medium / BruteForce (Python)
94. Balanced Binary Tree Solution Easy / Binary Tree (Python)
95. Cheapest Flights Within K Stops Solution Medium / Bellman Ford (Python)
96. Network Delay Time Solution Medium / Dijkstra’s Algorithm (Python)
97. Missing Number Solution Easy / Math/XOR (Python)
98. Merge Triplets to Form Target Triplet Solution Medium / Greedy (Python)
99. Pacific Atlantic Water Flow Solution Medium / DFS (Python)
100. Time Based Key-Value Store Solution Medium / Binary Search (Python)
101. Detect Squares Solution Medium / Hash Map (Python)