leetcode/README.md

LeetCode Solutions

🧠 Why This Repository Exists

I'm practicing to master data structures, algorithms, and problem-solving patterns. This repository serves as my personal learning journey through LeetCode problems, helping me:

• Build algorithmic thinking and problem-solving skills
• Master fundamental data structures (arrays, linked lists, trees, graphs, etc.)
• Learn advanced algorithms (dynamic programming, binary search, two pointers, etc.)
• Track my progress and identify areas for improvement
• Create a reference library of solutions for future review

✅ Progress Overview

Current Status

• Problems Solved: 90+ / 2000+ (LeetCode total)
• Success Rate: ~95%
• Streak: Active daily practice
• Languages: Python (primary), TypeScript (secondary)

Difficulty Breakdown

Difficulty	Count	Percentage
🟢 Easy	~40	44%
🟡 Medium	~45	50%
🔴 Hard	~5	6%

Recent Activity

• Last Solved: Multiple problems this week
• Focus Areas: Dynamic Programming, Graph Algorithms
• Next Goals: Advanced tree problems, system design concepts

🧩 Topics Covered

✅ Mastered

• Arrays & Strings - Two pointers, sliding window, prefix sums
• Hash Tables - Lookup optimization, frequency counting
• Binary Search - Standard and rotated array variations
• Two Pointers - Array manipulation, linked list operations
• Basic Dynamic Programming - Memoization, tabulation

🔄 In Progress

• Advanced DP - State compression, optimization techniques
• Graph Algorithms - BFS, DFS, topological sorting
• Tree Structures - Binary trees, BST operations
• Advanced Data Structures - Heaps, Tries, Union-Find

📚 Planned

• System Design - Scalability, distributed systems
• Advanced Algorithms - Segment trees, advanced graph algorithms
• Competitive Programming - Advanced optimization techniques

📋 Problem Checklist

Core Data Structures

Topic	Easy	Medium	Hard	Total
Arrays	15	20	2	37
Strings	8	12	1	21
Linked Lists	1	4	0	5
Trees	0	0	0	0
Graphs	0	2	0	2
Stacks/Queues	2	3	0	5

Algorithmic Techniques

Technique	Easy	Medium	Hard	Total
Hash Tables	8	12	0	20
Two Pointers	6	15	0	21
Binary Search	2	8	0	10
Dynamic Programming	0	8	0	8
Greedy	0	6	0	6
Backtracking	0	3	0	3
Sliding Window	1	1	0	2

Problem Categories

Category	Count	Mastery Level
Array Manipulation	25	⭐⭐⭐⭐⭐
String Processing	18	⭐⭐⭐⭐
Hash Table Usage	20	⭐⭐⭐⭐⭐
Binary Search	10	⭐⭐⭐⭐
Dynamic Programming	8	⭐⭐⭐
Two Pointers	21	⭐⭐⭐⭐⭐
Linked Lists	5	⭐⭐⭐
Graphs	2	⭐⭐
Stacks/Queues	5	⭐⭐⭐

🎯 Learning Roadmap

Phase 1: Fundamentals ✅

• Basic array operations
• String manipulation
• Hash table implementations
• Two pointer techniques
• Basic binary search

Phase 2: Intermediate 🔄

• Dynamic programming basics
• Linked list operations
• Stack and queue problems
• Greedy algorithms
• Tree traversal algorithms
• Graph basics (BFS/DFS)

Phase 3: Advanced 📚

• Advanced DP techniques
• Advanced tree structures
• Graph algorithms
• System design concepts
• Competitive programming

Phase 4: Mastery 🏆

• Advanced optimization
• Algorithm design
• Interview preparation
• Teaching others

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This repository contains my solutions to various LeetCode problems. Each solution is implemented in Python and follows a consistent structure.

📊 Statistics

• Total Problems Solved: 90+
• Languages: Python, TypeScript
• Difficulty Distribution: Easy, Medium, Hard

📁 Solutions Index

🔢 Arrays & Strings

Easy

• 1. Two Sum - Hash Table, Array
• 9. Palindrome Number - Math
• 13. Roman to Integer - Hash Table, Math, String
• 14. Longest Common Prefix - String, Trie
• 20. Valid Parentheses - Stack, String
• 21. Merge Two Sorted Lists - Linked List, Recursion
• 26. Remove Duplicates from Sorted Array - Array, Two Pointers
• 27. Remove Element - Array, Two Pointers
• 28. Find the Index of the First Occurrence in a String - String, Two Pointers
• 35. Search Insert Position - Array, Binary Search
• 66. Plus One - Array, Math
• 69. Sqrt(x) - Math, Binary Search
• 88. Merge Sorted Array - Array, Two Pointers
• 125. Valid Palindrome - String, Two Pointers
• 169. Majority Element - Array, Hash Table, Divide and Conquer
• 202. Happy Number - Hash Table, Math, Two Pointers
• 205. Isomorphic Strings - Hash Table, String
• 217. Contains Duplicate - Array, Hash Table, Sorting
• 219. Contains Duplicate II - Array, Hash Table, Sliding Window
• 242. Valid Anagram - String, Sorting, Hash Table
• 290. Word Pattern - Hash Table, String
• 383. Ransom Note - String, Hash Table, Counting
• 392. Is Subsequence - String, Two Pointers, Dynamic Programming
• 704. Binary Search - Array, Binary Search
• 1200. Minimum Absolute Difference - Array, Sorting
• 2053. Kth Distinct String in an Array - Array, Hash Table, String
• 2441. Largest Positive Integer That Exists With Its Negative - Array, Hash Table, Two Pointers

Medium

• 2. Add Two Numbers - Linked List, Math, Recursion
• 3. Longest Substring Without Repeating Characters - Hash Table, String, Sliding Window
• 3. Longest Substring Without Repeating Characters (TypeScript) - Hash Table, String, Sliding Window
• 4. Median of Two Sorted Arrays - Array, Binary Search, Divide and Conquer
• 5. Longest Palindromic Substring - String, Dynamic Programming
• 6. Zigzag Conversion - String
• 7. Reverse Integer - Math
• 10. Regular Expression Matching - String, Dynamic Programming, Recursion
• 11. Container With Most Water - Array, Two Pointers, Greedy
• 15. 3Sum - Array, Two Pointers, Sorting
• 22. Generate Parentheses - String, Dynamic Programming, Backtracking
• 36. Valid Sudoku - Array, Hash Table, Matrix
• 42. Trapping Rain Water - Array, Two Pointers, Dynamic Programming, Stack
• 45. Jump Game II - Array, Dynamic Programming, Greedy
• 50. Pow(x, n) - Math, Recursion
• 55. Jump Game - Array, Dynamic Programming, Greedy
• 74. Search a 2D Matrix - Array, Binary Search, Matrix
• 80. Remove Duplicates from Sorted Array II - Array, Two Pointers
• 89. Gray Code - Math, Backtracking, Bit Manipulation
• 90. Subsets II - Array, Backtracking, Bit Manipulation
• 91. Decode Ways - String, Dynamic Programming
• 92. Reverse Linked List II - Linked List
• 121. Best Time to Buy and Sell Stock - Array, Dynamic Programming
• 122. Best Time to Buy and Sell Stock II - Array, Dynamic Programming, Greedy
• 128. Longest Consecutive Sequence - Array, Hash Table, Union Find
• 135. Candy - Array, Greedy
• 141. Linked List Cycle - Hash Table, Linked List, Two Pointers
• 149. Max Points on a Line - Array, Hash Table, Math, Geometry
• 150. Evaluate Reverse Polish Notation - Array, Math, Stack
• 153. Find Minimum in Rotated Sorted Array - Array, Binary Search
• 155. Min Stack - Stack, Design
• 167. Two Sum II - Input Array Is Sorted - Array, Two Pointers, Binary Search
• 172. Factorial Trailing Zeroes - Math
• 189. Rotate Array - Array, Math, Two Pointers
• 206. Reverse Linked List - Linked List, Recursion
• 228. Summary Ranges - Array
• 238. Product of Array Except Self - Array, Prefix Sum
• 246. Strobogrammatic Number - Hash Table, Two Pointers, String
• 248. Strobogrammatic Number III - Math, Recursion
• 243. Shortest Word Distance - Array, String
• 244. Shortest Word Distance II - Array, Hash Table, Design, Two Pointers
• 245. Shortest Word Distance III - Array, String
• 875. Koko Eating Bananas - Array, Binary Search
• 990. Satisfiability of Equality Equations - Array, Union Find, Graph
• 1298. Maximum Candies You Can Get from Boxes - Breadth-First Search, Array
• 1820. Maximum Number of Accepted Invitations - Graph, Backtracking
• 2040. Kth Smallest Product of Two Sorted Arrays - Array, Binary Search
• 2116. Check if a Parentheses String Can Be Valid - String, Stack, Greedy
• 2294. Partition Array Such That Maximum Difference Is K - Array, Greedy, Sorting
• 2616. Minimize the Maximum Difference of Pairs - Array, Binary Search, Greedy
• 2966. Divide Array Into Arrays With Max Difference - Array, Greedy, Sorting
• 3442. Maximum Difference Between Even and Odd Frequency I - Array, Hash Table
• 3445. Maximum Difference Between Even and Odd Frequency II - Array, Hash Table

🔗 Linked Lists

• 2. Add Two Numbers - Linked List, Math, Recursion
• 21. Merge Two Sorted Lists - Linked List, Recursion
• 92. Reverse Linked List II - Linked List
• 141. Linked List Cycle - Hash Table, Linked List, Two Pointers
• 206. Reverse Linked List - Linked List, Recursion

🌳 Trees & Graphs

• 1298. Maximum Candies You Can Get from Boxes - Breadth-First Search, Array
• 1820. Maximum Number of Accepted Invitations - Graph, Backtracking
• 990. Satisfiability of Equality Equations - Array, Union Find, Graph

🔍 Binary Search

• 4. Median of Two Sorted Arrays - Array, Binary Search, Divide and Conquer
• 35. Search Insert Position - Array, Binary Search
• 50. Pow(x, n) - Math, Recursion
• 69. Sqrt(x) - Math, Binary Search
• 74. Search a 2D Matrix - Array, Binary Search, Matrix
• 153. Find Minimum in Rotated Sorted Array - Array, Binary Search
• 167. Two Sum II - Input Array Is Sorted - Array, Two Pointers, Binary Search
• 704. Binary Search - Array, Binary Search
• 875. Koko Eating Bananas - Array, Binary Search
• 2040. Kth Smallest Product of Two Sorted Arrays - Array, Binary Search
• 2616. Minimize the Maximum Difference of Pairs - Array, Binary Search, Greedy

🧮 Dynamic Programming

• 5. Longest Palindromic Substring - String, Dynamic Programming
• 10. Regular Expression Matching - String, Dynamic Programming, Recursion
• 22. Generate Parentheses - String, Dynamic Programming, Backtracking
• 42. Trapping Rain Water - Array, Two Pointers, Dynamic Programming, Stack
• 45. Jump Game II - Array, Dynamic Programming, Greedy
• 55. Jump Game - Array, Dynamic Programming, Greedy
• 91. Decode Ways - String, Dynamic Programming
• 121. Best Time to Buy and Sell Stock - Array, Dynamic Programming
• 122. Best Time to Buy and Sell Stock II - Array, Dynamic Programming, Greedy
• 128. Longest Consecutive Sequence - Array, Hash Table, Union Find
• 135. Candy - Array, Greedy
• 392. Is Subsequence - String, Two Pointers, Dynamic Programming

🎯 Two Pointers

• 3. Longest Substring Without Repeating Characters - Hash Table, String, Sliding Window
• 11. Container With Most Water - Array, Two Pointers, Greedy
• 15. 3Sum - Array, Two Pointers, Sorting
• 26. Remove Duplicates from Sorted Array - Array, Two Pointers
• 27. Remove Element - Array, Two Pointers
• 28. Find the Index of the First Occurrence in a String - String, Two Pointers
• 42. Trapping Rain Water - Array, Two Pointers, Dynamic Programming, Stack
• 80. Remove Duplicates from Sorted Array II - Array, Two Pointers
• 88. Merge Sorted Array - Array, Two Pointers
• 125. Valid Palindrome - String, Two Pointers
• 141. Linked List Cycle - Hash Table, Linked List, Two Pointers
• 167. Two Sum II - Input Array Is Sorted - Array, Two Pointers, Binary Search
• 189. Rotate Array - Array, Math, Two Pointers
• 202. Happy Number - Hash Table, Math, Two Pointers
• 219. Contains Duplicate II - Array, Hash Table, Sliding Window
• 243. Shortest Word Distance - Array, String
• 244. Shortest Word Distance II - Array, Hash Table, Design, Two Pointers
• 245. Shortest Word Distance III - Array, String
• 246. Strobogrammatic Number - Hash Table, Two Pointers, String
• 392. Is Subsequence - String, Two Pointers, Dynamic Programming
• 2441. Largest Positive Integer That Exists With Its Negative - Array, Hash Table, Two Pointers

🗃️ Hash Tables

• 1. Two Sum - Hash Table, Array
• 13. Roman to Integer - Hash Table, Math, String
• 20. Valid Parentheses - Stack, String
• 36. Valid Sudoku - Array, Hash Table, Matrix
• 141. Linked List Cycle - Hash Table, Linked List, Two Pointers
• 149. Max Points on a Line - Array, Hash Table, Math, Geometry
• 169. Majority Element - Array, Hash Table, Divide and Conquer
• 202. Happy Number - Hash Table, Math, Two Pointers
• 205. Isomorphic Strings - Hash Table, String
• 217. Contains Duplicate - Array, Hash Table, Sorting
• 219. Contains Duplicate II - Array, Hash Table, Sliding Window
• 242. Valid Anagram - String, Sorting, Hash Table
• 243. Shortest Word Distance - Array, String
• 244. Shortest Word Distance II - Array, Hash Table, Design, Two Pointers
• 246. Strobogrammatic Number - Hash Table, Two Pointers, String
• 290. Word Pattern - Hash Table, String
• 383. Ransom Note - String, Hash Table, Counting
• 128. Longest Consecutive Sequence - Array, Hash Table, Union Find
• 2053. Kth Distinct String in an Array - Array, Hash Table, String
• 2441. Largest Positive Integer That Exists With Its Negative - Array, Hash Table, Two Pointers
• 3442. Maximum Difference Between Even and Odd Frequency I - Array, Hash Table
• 3445. Maximum Difference Between Even and Odd Frequency II - Array, Hash Table

📚 Stacks & Queues

• 20. Valid Parentheses - Stack, String
• 42. Trapping Rain Water - Array, Two Pointers, Dynamic Programming, Stack
• 150. Evaluate Reverse Polish Notation - Array, Math, Stack
• 155. Min Stack - Stack, Design
• 2116. Check if a Parentheses String Can Be Valid - String, Stack, Greedy

🔄 Backtracking

• 22. Generate Parentheses - String, Dynamic Programming, Backtracking
• 89. Gray Code - Math, Backtracking, Bit Manipulation
• 90. Subsets II - Array, Backtracking, Bit Manipulation
• 1820. Maximum Number of Accepted Invitations - Graph, Backtracking

🎲 Greedy

• 11. Container With Most Water - Array, Two Pointers, Greedy
• 45. Jump Game II - Array, Dynamic Programming, Greedy
• 55. Jump Game - Array, Dynamic Programming, Greedy
• 122. Best Time to Buy and Sell Stock II - Array, Dynamic Programming, Greedy
• 135. Candy - Array, Greedy
• 2116. Check if a Parentheses String Can Be Valid - String, Stack, Greedy
• 2294. Partition Array Such That Maximum Difference Is K - Array, Greedy, Sorting
• 2616. Minimize the Maximum Difference of Pairs - Array, Binary Search, Greedy
• 2966. Divide Array Into Arrays With Max Difference - Array, Greedy, Sorting

🔢 Math

• 7. Reverse Integer - Math
• 9. Palindrome Number - Math
• 13. Roman to Integer - Hash Table, Math, String
• 50. Pow(x, n) - Math, Recursion
• 66. Plus One - Array, Math
• 69. Sqrt(x) - Math, Binary Search
• 89. Gray Code - Math, Backtracking, Bit Manipulation
• 149. Max Points on a Line - Array, Hash Table, Math, Geometry
• 172. Factorial Trailing Zeroes - Math
• 189. Rotate Array - Array, Math, Two Pointers
• 202. Happy Number - Hash Table, Math, Two Pointers
• 150. Evaluate Reverse Polish Notation - Array, Math, Stack

🧮 Bit Manipulation

• 89. Gray Code - Math, Backtracking, Bit Manipulation
• 90. Subsets II - Array, Backtracking, Bit Manipulation

🏗️ Design

• 155. Min Stack - Stack, Design
• 244. Shortest Word Distance II - Array, Hash Table, Design, Two Pointers

🔗 Union Find

• 128. Longest Consecutive Sequence - Array, Hash Table, Union Find
• 990. Satisfiability of Equality Equations - Array, Union Find, Graph

📊 Sorting

• 15. 3Sum - Array, Two Pointers, Sorting
• 80. Remove Duplicates from Sorted Array II - Array, Two Pointers
• 88. Merge Sorted Array - Array, Two Pointers
• 1200. Minimum Absolute Difference - Array, Sorting
• 217. Contains Duplicate - Array, Hash Table, Sorting
• 242. Valid Anagram - String, Sorting, Hash Table
• 2294. Partition Array Such That Maximum Difference Is K - Array, Greedy, Sorting
• 2966. Divide Array Into Arrays With Max Difference - Array, Greedy, Sorting

🔄 Recursion

• 2. Add Two Numbers - Linked List, Math, Recursion
• 10. Regular Expression Matching - String, Dynamic Programming, Recursion
• 21. Merge Two Sorted Lists - Linked List, Recursion
• 22. Generate Parentheses - String, Dynamic Programming, Backtracking
• 50. Pow(x, n) - Math, Recursion
• 206. Reverse Linked List - Linked List, Recursion
• 248. Strobogrammatic Number III - Math, Recursion

🎯 Sliding Window

• 3. Longest Substring Without Repeating Characters - Hash Table, String, Sliding Window
• 219. Contains Duplicate II - Array, Hash Table, Sliding Window

📐 Geometry

• 149. Max Points on a Line - Array, Hash Table, Math, Geometry

🔍 Divide and Conquer

• 4. Median of Two Sorted Arrays - Array, Binary Search, Divide and Conquer
• 169. Majority Element - Array, Hash Table, Divide and Conquer

📝 String Manipulation

• 3. Longest Substring Without Repeating Characters - Hash Table, String, Sliding Window
• 5. Longest Palindromic Substring - String, Dynamic Programming
• 6. Zigzag Conversion - String
• 10. Regular Expression Matching - String, Dynamic Programming, Recursion
• 13. Roman to Integer - Hash Table, Math, String
• 14. Longest Common Prefix - String, Trie
• 20. Valid Parentheses - Stack, String
• 22. Generate Parentheses - String, Dynamic Programming, Backtracking
• 28. Find the Index of the First Occurrence in a String - String, Two Pointers
• 125. Valid Palindrome - String, Two Pointers
• 205. Isomorphic Strings - Hash Table, String
• 242. Valid Anagram - String, Sorting, Hash Table
• 246. Strobogrammatic Number - Hash Table, Two Pointers, String
• 248. Strobogrammatic Number III - Math, Recursion
• 290. Word Pattern - Hash Table, String
• 383. Ransom Note - String, Hash Table, Counting
• 392. Is Subsequence - String, Two Pointers, Dynamic Programming
• 91. Decode Ways - String, Dynamic Programming
• 2116. Check if a Parentheses String Can Be Valid - String, Stack, Greedy

📊 Matrix

• 36. Valid Sudoku - Array, Hash Table, Matrix
• 74. Search a 2D Matrix - Array, Binary Search, Matrix

🔢 Counting

• 383. Ransom Note - String, Hash Table, Counting

🌐 Breadth-First Search

• 1298. Maximum Candies You Can Get from Boxes - Breadth-First Search, Array

📈 Progress Tracking

Difficulty Distribution

• Easy: ~40 problems
• Medium: ~45 problems
• Hard: ~5 problems

Top Problem Types

1. Arrays & Strings - Most common
2. Hash Tables - Frequently used technique
3. Two Pointers - Efficient array manipulation
4. Binary Search - Optimization problems
5. Dynamic Programming - Complex problem solving

🛠️ Solution Structure

Each solution follows a consistent structure:

• Standard library imports
• Type hints for better code clarity
• Solution class with required method
• Clean, readable implementation
• Proper comments and documentation

🎯 Learning Focus Areas

Based on the solutions, key areas of expertise include:

• Array manipulation and two-pointer techniques
• Hash table optimization for lookups
• Binary search for efficient searching
• Dynamic programming for complex problems
• String manipulation and palindrome problems
• Linked list operations and cycle detection

📚 Resources

• LeetCode Problem Set
• LeetCode Profile

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This index is automatically generated and organized by problem categories and difficulty levels. Each solution includes the relevant tags and techniques used.