LeetCode Solutions - Comprehensive Collection

This repository contains solutions to LeetCode problems organized by difficulty level (Easy, Medium, Hard). All solutions are implemented in JavaScript with Python implementations included as comments.

Final 200 - Easy

Number	Problem Name	Solution
1	Two Sum	Two Sum
2	Valid Palindrome	Valid Palindrome
3	Valid Parentheses	Valid Parentheses
4	Merge Two Sorted Lists	Merge Two Sorted Lists
5	Reverse Linked List	Reverse Linked List
6	Linked List Cycle	Linked List Cycle
7	Middle of the Linked List	Middle of the Linked List
8	Palindrome Linked List	Palindrome Linked List
9	Invert Binary Tree	Invert Binary Tree
10	Same Tree	Same Tree
11	Symmetric Tree	Symmetric Tree
12	Maximum Depth of Binary Tree	Maximum Depth of Binary Tree
13	Valid Anagram	Valid Anagram
14	Ransom Note	Ransom Note
15	Isomorphic Strings	Isomorphic Strings
16	Contains Duplicate II	Contains Duplicate II
17	Happy Number	Happy Number
18	Word Pattern	Word Pattern
19	Summary Ranges	Summary Ranges
20	Remove Duplicates from Sorted Array	Remove Duplicates
21	Remove Element	Remove Element
22	Merge Sorted Array	Merge Sorted Array
23	Majority Element	Majority Element
24	Best Time to Buy and Sell Stock	Stock I
25	Best Time to Buy and Sell Stock II	Stock II
26	Is Subsequence	Is Subsequence
27	Plus One	Plus One
28	Palindrome Number	Palindrome Number
29	Single Number	Single Number
30	Longest Common Prefix	Longest Common Prefix
31	Length of Last Word	Length of Last Word
32	Sqrt(x)	Sqrt(x)
33	Number of 1 Bits	Number of 1 Bits
34	Find the Index of the First Occurrence in a String	Find First Occurrence
35	Reverse Bits	Reverse Bits
36	Add Binary	Add Binary
37	Search Insert Position	Search Insert Position
38	Counting Bits	Counting Bits
39	Two Sum II - Input Array Is Sorted	Two Sum II
40	Missing Number	Missing Number
41	Climbing Stairs	Climbing Stairs
42	Roman to Integer	Roman to Integer

Final 200 - Medium

Number	Problem Name	Solution
1	3sum	3sum
2	Container With Most Water	Container With Most Water
3	Remove Nth Node From End of List	Remove Nth
4	Copy List with Random Pointer	Copy List
5	Add Two Numbers	Add Two Numbers
6	Add Two Numbers II	Add Two Numbers II
7	LRU Cache	LRU Cache
8	Lowest Common Ancestor of a Binary Search Tree	LCA of BST
9	Lowest Common Ancestor of a Binary Tree	LCA of BT
10	Binary Tree Right Side View	Right Side View
11	Binary Tree Level Order Traversal	Level Order
12	Binary Tree Zigzag Level Order Traversal	Zigzag Level Order
13	Validate Binary Search Tree	Validate BST
14	Kth Smallest Element in a BST	Kth Smallest BST
15	Construct Binary Tree from Preorder and Inorder Traversal	Construct Pre+In
16	Construct Binary Tree from Inorder and Postorder Traversal	Construct In+Post
17	Populating Next Right Pointers in Each Node II	Next Right II
18	Flatten Binary Tree to Linked List	Flatten BT
19	Path Sum II	Path Sum II
20	Sum Root to Leaf Numbers	Sum Root to Leaf
21	Binary Search Tree Iterator	BST Iterator
22	Count Complete Tree Nodes	Count Nodes
23	Number of Islands	Number of Islands
24	Surrounded Regions	Surrounded Regions
25	Clone Graph	Clone Graph
26	Course Schedule	Course Schedule
27	Evaluate Division	Evaluate Division
28	Coin Change	Coin Change
29	Longest Increasing Subsequence	LIS
30	Min Cost Climbing Stairs	Min Cost Climbing
31	Maximum Product Subarray	Max Product
32	Minimum Size Subarray Sum	Min Subarray Sum
33	Longest Substring Without Repeating Characters	Longest Substring
34	Find First and Last Position of Element in Sorted Array	Find First Last
35	Search a 2D Matrix	Search 2D Matrix
36	Search in Rotated Sorted Array	Search Rotated
37	Find Minimum in Rotated Sorted Array	Find Min Rotated
38	Find Peak Element	Find Peak
39	Simplify Path	Simplify Path
40	Min Stack	Min Stack
41	Valid Sudoku	Valid Sudoku
42	Spiral Matrix	Spiral Matrix
43	Rotate Image	Rotate Image
44	Set Matrix Zeroes	Set Matrix Zeroes
45	Game of Life	Game of Life
46	Group Anagrams	Group Anagrams
47	Longest Consecutive Sequence	Longest Consecutive
48	4Sum	4Sum
49	Product of Array Except Self	Product Except Self
50	Jump Game	Jump Game
51	Jump Game II	Jump Game II
52	H-Index	H-Index
53	Insert Delete GetRandom O(1)	RandomizedSet
54	Gas Station	Gas Station
55	Candy	Candy
56	Reverse Words in a String	Reverse Words
57	Zigzag Conversion	Zigzag Conversion
58	Minimum Number of Arrows to Burst Balloons	Min Arrows
59	Merge Intervals	Merge Intervals
60	Insert Interval	Insert Interval
61	Remove Duplicates from Sorted Array II	Remove Duplicates II
62	Evaluate Reverse Polish Notation	Evaluate RPN
63	House Robber	House Robber

Final 200 - Hard

Number	Problem Name	Solution
1	Basic Calculator	Basic Calculator
2	Trapping Rain Water	Trapping Rain Water
3	Word Search II	Word Search II
4	Median of Two Sorted Arrays	Median of Two Sorted Arrays
5	Reverse Nodes in k-Group	Reverse Nodes in k-Group
6	Max Points on a Line	Max Points on a Line

List of Topic-wise Leetcode Problems:

➤ Array Manipulation & Sorting

1. Sort Colors ✅
2. Find All Duplicates in an Array ✅
3. Missing Number ✅
4. Find Duplicate Number ✅
5. Remove Duplicates from Sorted Array ✅
6. Remove Duplicates from Sorted Array II ✅
7. Find K Closest Elements ✅
8. Find Missing Positive Integer
9. Find Peak Element ✅
10. Find the Maximum Sum Subarray (Kadane's Algorithm) ✅
11. Kth Largest Element in an Array ✅
12. Top K Frequent Elements ✅
13. Longest Consecutive Sequence ✅
14. Find the Smallest Range Covering Elements from K Lists
15. Heapsort
16. Maximum Gap
17. Wiggle Sort II

➤ Searching Algorithms (Binary Search & Variants)

1. Search in Rotated Sorted Array
2. Search in Rotated Sorted Array II
3. Find First and Last Position in a Sorted Array
4. Search Insert Position
5. Find Minimum in Rotated Sorted Array
6. Median of Two Sorted Arrays ✅
7. Search a 2D Matrix

➤ Sliding Window & Substring Problems

1. Valid Palindrome ✅
2. Longest Substring Without Repeating Characters ✅
3. Find All Anagrams in a String ✅
4. Longest Palindromic Substring
5. Minimum Window Substring

➤ Intervals & Merging Problems

1. Summary Ranges ✅
2. Merge Intervals ✅
3. Insert Interval ✅
4. Minimum Absolute Difference
5. Minimum Number of Arrows to Burst Balloons ✅
6. Maximum Number of Events That Can Be Attended
7. Intersection of Two Arrays II

➤ Matrix Problems

1. Rotate Image
2. Set Matrix Zeroes
3. Spiral Matrix
4. Word Search

➤ Array/String Misc

1. Find All Anagrams in a String ✅
2. Subarray Sum Equals K ✅
3. Minimum Size Subarray Sum ✅
4. Maximum Product Subarray ✅
5. Find First and Last Position in a Sorted Array
6. Count and Say ✅

➤ Hashmaps

1. Valid Anagram ✅
2. Ransom Note ✅
3. Group Anagrams ✅
4. Isomorphic Strings ✅
5. Two Sum ✅
6. Contains Duplicate II ✅
7. Happy Number ✅

➤ Stacks and Queues

1. Valid Parentheses ✅
2. Min Stack ✅
3. Backspace String Compare
4. Simplify Path ✅
5. Evaluate Reverse Polish Notation ✅
6. Daily Temperatures
7. Decode String
8. Basic Calculator ✅
9. Car Fleet
10. Generate Parentheses
11. Asteroid Collision
12. Basic Calculator II
13. Maximum Frequency Stack
14. Longest Valid Parentheses
15. Largest Rectangle in Histogram

➤ Linked Lists

1. Reverse Linked List ✅
2. Merge Two Sorted Lists ✅
3. Linked List Cycle ✅
4. Middle of the Linked List ✅
5. Palindrome Linked List ✅
6. Remove Nth Node From End of List ✅
7. Copy List with Random Pointer ✅
8. Add Two Numbers ✅
9. Reorder List ✅
10. Swap Nodes in Pairs ✅
11. Odd Even Linked List ✅
12. Sort List ✅
13. Reverse Nodes in k-Group ✅
14. Merge K Sorted Lists ✅
15. LRU Cache ✅

➤ Trees

1. Invert Binary Tree ✅
2. Same Tree ✅
3. Symmetric Tree ✅
4. Maximum Depth of Binary Tree
5. Balanced Binary Tree
6. Subtree of Another Tree
7. Lowest Common Ancestor of a Binary Search Tree
8. Diameter of Binary Tree
9. Path Sum
10. Count Complete Tree Nodes
11. Validate Binary Search Tree ✅
12. Kth Smallest Element in a BST ✅
13. Construct Binary Tree from Preorder and Inorder Traversal
14. Binary Tree Level Order Traversal ✅
15. Binary Tree Zigzag Level Order Traversal
16. Binary Tree Right Side View
17. Count Good Nodes in Binary Tree
18. Flatten Binary Tree to Linked List
19. Path Sum II
20. Populating Next Right Pointers in Each Node II
21. Sum Root to Leaf Numbers
22. Minimum Absolute Difference in BST
23. Binary Tree Maximum Path Sum
24. Serialize and Deserialize Binary Tree
25. Recover Binary Search Tree

➤ Trie

1. Implement Trie ✅
2. Design Add and Search Words Data Structure ✅
3. Longest Word in Dictionary ✅
4. Replace Words ✅
5. Word Search II ✅

➤ Heap

1. Kth Largest Element in a Stream
2. Last Stone Weight
3. Kth Largest Element in an Array ✅
4. K Closest Points to Origin
5. Task Scheduler
6. Top K Frequent Words
7. Find K Closest Elements ✅
8. Merge K Sorted Lists
9. Find Median from Data Stream
10. Sliding Window Median

➤ Backtracking

1. N-Queens
2. Sudoku Solver
3. Word Search
4. Subsets
5. Permutations
6. Combination Sum
7. Generate Parentheses
8. Palindrome Partitioning
9. Letter Combinations of a Phone Number
10. Restore IP Addresses

➤ Graphs

1. Flood Fill
2. Number of Islands
3. Max Area of Island
4. Clone Graph
5. Course Schedule
6. Course Schedule II
7. Pacific Atlantic Water Flow
8. Rotting Oranges
9. Surrounded Regions
10. Walls and Gates
11. Graph Valid Tree
12. Number of Connected Components in an Undirected Graph
13. Redundant Connection
14. Find Eventual Safe States
15. Network Delay Time
16. Path with Maximum Probability
17. Word Ladder
18. Shortest Path in a Grid with Obstacles Elimination
19. Alien Dictionary
20. Find Strongly Connected Components

➤ Dynamic Programming

1. Climbing Stairs ✅
2. Coin Change ✅
3. Word Break ✅
4. House Robber ✅
5. Paint House
6. Unique Paths II
7. 0/1 Knapsack Problem
8. Palindromic Substrings
9. Decode Ways
10. Unique Paths
11. Shortest Common Supersequence
12. Interleaving String
13. House Robber II
14. Minimum Path Sum
15. Maximal Square
16. Longest Increasing Subsequence
17. Can I Win
18. Ones and Zeroes
19. Longest Palindromic Subsequence
20. Partition Equal Subset Sum / Partition to K Equal Sum Subset
21. Cheapest Flights Within K Stop
22. Longest Arithmetic Sequence
23. Last Stone Weight II
24. Filling Bookcase Shelves
25. Longest Common Subsequence
26. Dice Roll Sum
27. Longest Valid Parentheses
28. Wildcard Matching
29. Edit Distance
30. Best Time to Buy and Sell Stocks
31. Burst Balloons
32. Minimum Cost to Merge Stones
33. Minimum Difficulty of a Job Schedule

➤ Greedy Algorithms

1. Activity Selection Problem
2. Huffman Encoding
3. Minimum Platforms
4. Job Sequencing Problem
5. Jump Game
6. Gas Station ✅
7. Partition Labels
8. Dijkstra's Algorithm
9. Trapping Rain Water ✅
10. Largest Rectangle in Histogram
11. Container With Most Water ✅
12. Reorganize String

➤ Bit Manipulation, Maths, Misc

1. Single Number
2. Number of 1 Bits
3. Counting Bits
4. Reverse Bits
5. Add Binary
6. Divide Two Integers
7. Single Number II
8. Bitwise AND of Numbers Range
9. Palindrome Number
10. Plus One
11. Pow(x, n)
12. Factorial Trailing Zeroes
13. Multiply Strings