Hacktoberfest 2025 - LeetCode 75 Solutions 🚀

A repository dedicated to helping developers contribute to Hacktoberfest 2025 by solving the famous LeetCode 75 problems. This is a perfect place for beginners and experienced developers alike to practice algorithms and data structures while participating in Hacktoberfest!

📋 What is LeetCode 75?

LeetCode 75 is a curated list of 75 essential coding problems that cover fundamental data structures and algorithms frequently asked in technical interviews. This collection is designed to build your problem-solving skills progressively.

🎯 How to Contribute

Step 1: Fork this Repository

Click the "Fork" button at the top right of this page to create your own copy.

Step 2: Find a Problem

Browse the list of problems below and pick one that hasn't been solved yet, or add your solution to an existing problem.

Step 3: Add Your Solution

• Create a new file in the appropriate topic folder
• Naming convention: QuestionName_username.extension
• Example: Two_Sum_johndoe.py or Reverse_Linked_List_janedoe.java

Step 4: Submit a Pull Request

• Create a pull request from your forked repository to this main repository
• Make sure your PR description clearly indicates which problem you've solved
• PRs will be reviewed and merged regularly

🧩 Problem Categories

Array / String

• Merge Strings Alternately
• Greatest Common Divisor of Strings
• Kids With the Greatest Number of Candies
• Can Place Flowers
• Reverse Vowels of a String
• Reverse Words in a String
• Product of Array Except Self
• Increasing Triplet Subsequence
• String Compression

Two Pointers

• Move Zeroes
• Is Subsequence
• Container With Most Water
• Max Number of K-Sum Pairs

Sliding Window

• Maximum Average Subarray I
• Maximum Number of Vowels in a Substring of Given Length
• Max Consecutive Ones III
• Longest Subarray of 1's After Deleting One Element

Prefix Sum

• Find the Highest Altitude
• Find Pivot Index

Hash Map / Set

• Find the Difference of Two Arrays
• Unique Number of Occurrences
• Determine if Two Strings Are Close
• Equal Row and Column Pairs

Stack

• Asteroid Collision
• Decode String
• Removing Stars From a String

Queue

• Number of Recent Calls
• Dota2 Senate
• Reveal Cards In Increasing Order

Linked List

• Delete the Middle Node of a Linked List
• Odd Even Linked List
• Reverse Linked List
• Maximum Twin Sum of a Linked List

Binary Search

• Binary Search
• Search a 2D Matrix
• Koko Eating Bananas
• Find Peak Element
• Minimum Number of Days to Make m Bouquets

Binary Tree - DFS

• Root Equals Sum of Children
• Count Good Nodes in Binary Tree
• Path Sum III
• Longest ZigZag Path in a Binary Tree
• Lowest Common Ancestor of a Binary Tree
• Maximum Level Sum of a Binary Tree

Binary Tree - BFS

• Binary Tree Right Side View
• Maximum Width of Binary Tree

Graph - DFS/BFS

• Keys and Rooms
• Number of Provinces
• Reorder Routes to Make All Paths Lead to the City Zero
• Evaluate Division
• Nearest Exit from Entrance in Maze

Heap / Priority Queue

• Kth Largest Element in a Stream
• Last Stone Weight
• K Closest Points to Origin
• Smallest Number in Infinite Set
• Maximum Subsequence Score
• Total Cost to Hire K Workers

Binary Search Tree (BST)

• Search in a Binary Search Tree
• Delete Node in a BST
• Trim a BST
• Lowest Common Ancestor of a Binary Search Tree

Backtracking

• Subsets
• Combination Sum III
• Letter Combinations of a Phone Number
• N-Queens

Trie (Prefix Tree)

• Implement Trie (Prefix Tree)
• Search Suggestions System
• Word Search II

Intervals

• Non-overlapping Intervals
• Minimum Number of Arrows to Burst Balloons

Dynamic Programming - 1D

• N-th Tribonacci Number
• Min Cost Climbing Stairs
• House Robber
• House Robber II
• Longest Palindromic Substring
• Palindromic Substrings

Dynamic Programming - Multidimensional

• Unique Paths
• Longest Common Subsequence
• Best Time to Buy and Sell Stock with Transaction Fee
• Edit Distance
• Coin Change
• Coin Change II
• Maximum Profit in Job Scheduling

Bit Manipulation

• Counting Bits
• Single Number
• Minimum Flips to Make a OR b Equal to c

💻 Supported Languages

We welcome solutions in any programming language! Some popular choices:

• Python (.py)
• Java (.java)
• C++ (.cpp)
• JavaScript (.js)
• TypeScript (.ts)
• Go (.go)
• Rust (.rs)
• C# (.cs)
• And many more!

📝 Contribution Guidelines

1. One PR per problem: Please submit separate PRs for different problems
2. Quality over quantity: Well-commented, efficient solutions are preferred
3. Test your code: Make sure your solution passes all test cases
4. Follow naming conventions: Use the format QuestionName_username.extension
5. Add comments: Explain your approach and time/space complexity
6. No duplicate solutions: Check if a problem already has a solution in your language before submitting

🏆 Hacktoberfest Rules

• Sign up on the Hacktoberfest website
• Make 4 valid pull requests between October 1-31
• PRs must be in a participating public repository
• PRs must be approved by maintainers to count

🤝 Code of Conduct

Please be respectful and constructive in all interactions. We're here to learn and help each other grow as developers.

📊 Progress Tracking

Check the checkboxes above to see which problems have been solved! The list will be updated as contributions come in.

🆘 Need Help?

• Check existing solutions for reference
• Open an issue if you have questions
• Join the discussion in pull requests

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Happy Coding! 🎉 Let's make Hacktoberfest 2025 amazing!

Remember: The goal is learning and collaboration, not just completing challenges.