GFG Problems — DSA Solutions in C++

A curated collection of solved Data Structures & Algorithms problems from GeeksforGeeks, including Problem of the Day (POTD) submissions — all implemented in C++.

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Table of Contents

• About This Repository
• Repository Structure
• Folder Breakdown
  • School Problems
  • Basic Problems
  • Easy Problems
  • Medium Problems
  • Hard Problems
• Topics Covered
• How to Contribute
• Git Hooks Setup
• Naming Convention
• License

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About This Repository

This repository contains solutions for GFG problems organized by difficulty level. Each file is a self-contained C++ solution to a single problem. The goal is to:

• Build a reference library for common DSA patterns
• Track progress across difficulty levels
• Help others learn by reading clean, working solutions

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Browse by Difficulty

Folder	Description
🏫 School Problems	Foundational math, strings, I/O
🔵 Basic Problems	Arrays, linked lists, trees, basic patterns
🟢 Easy Problems	Sorting, searching, BST, stack, queue
🟡 Medium Problems	DP, graphs, advanced trees, sliding window
🔴 Hard Problems	Complex DP, advanced graphs, segment trees

Repository Structure

GFG-Problems/
├── School Problems/      # Foundational math, strings, I/O
├── Basic Problems/       # Arrays, linked lists, trees, basic patterns
├── Easy Problems/        # Sorting, searching, BST, stack, queue
├── Medium Problems/      # DP, graphs, advanced trees, sliding window
├── Hard Problems/        # Complex DP, advanced graphs, segment trees
└── README.md

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Folder Breakdown

🏫 School Problems

Count: 80+ problems

Beginner-level problems covering C++ fundamentals, basic math, and string manipulation.

Topic	Example Problems
Math & Numbers	Armstrong Number, Palindrome of Number, Perfect Number, Simple Interest, GCD, nPr
Strings	Reverse A String, Remove Vowels, Lower/Upper Case, Count Camel Case Characters
Arrays & Matrix	Matrix Multiplication, Transpose 2D Matrix, Sum of Diagonals, Mean/Median of Array
Patterns	Printing Pattern Set 1, Triangle Shrinking Downwards, Pattern of Strings
Linked Lists	Print Linked List Elements
Miscellaneous	Series of AP/GP, Swap Kth Element, Combinational Logic, Java Switch Case

📁 Path: School Problems

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🔵 Basic Problems

Count: 85+ problems

Covers core data structures and foundational algorithms.

Topic	Example Problems
Arrays	Missing Number, Binary Array Sorting, Cyclically Rotate Array, Count Pair Sum
Strings	Anagram of String, Implement strstr, Merge Two Strings, Print First Letter of Every Word
Linked Lists	Linked List Insertion, Insert in Middle, Node at Given Index, Find Sum of Last N Nodes
Trees	Inorder/Preorder/Postorder Traversal, Count Leaves, Minimum Element in BST
Stack	Implement Stack using Array
Searching	Binary Search, First and Last Occurrences of X
Math	LCM and GCD, Power of 2, Power of Four, Factorial, Fibonacci
Patterns	Pattern 1–13 (multiple star/number patterns)
Miscellaneous	Leap Year, Logical Operators, C++ STL Vector

📁 Path: Basic Problems

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🟢 Easy Problems

Count: 130+ problems

Introduces classic algorithm patterns and more complex data structures.

Topic	Example Problems
Arrays	Move Zeroes to End, Rotate Array, Sort 0-1-2, Equilibrium Point, Second Largest
Strings	Palindrome String, Panagram Checking, Run Length Encoding, Reverse Words
Linked Lists	Detect Loop, Reverse Linked List, Merge Sorted LL, Delete Middle Node
Trees	Height of Binary Tree, Left/Right View, Level Order Traversal, Mirror Tree
BST	Check for BST, Kth Largest in BST, Print BST Elements in Range
Sorting	Bubble Sort, Selection Sort
Stack & Queue	Parentheses Checker, Delete Middle of Stack, Two Stacks
Searching	Binary Search variants, Floor in Sorted Array, Find Transition Point
Math	Juggler Sequence, Padovan Sequence, Nth Fibonacci Number
Matrix	Search in Matrix, Print Matrix in Snake Pattern, Unique Rows in Boolean Matrix
Patterns	Pattern 2–21 (various shapes)

📁 Path: Easy Problems

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🟡 Medium Problems

Count: 160+ problems

Covers advanced techniques such as dynamic programming, greedy algorithms, and complex tree/graph operations.

Topic	Example Problems
Dynamic Programming	0/1 Knapsack, Longest Common Substring, Gold Mine, Pascal Triangle, Count Ways to Nth Stair
Greedy	Job Sequencing, Minimum Cost of Ropes, N Meetings in One Room, Maximum Tip Calculator
Linked Lists	Palindrome LL, Reverse in Groups, Flatten LL, Clone with Random Pointer (see Hard)
Trees	Diameter of Binary Tree, Diagonal Sum, Ancestors in BT, Boundary Traversal
BST	Lowest Common Ancestor, Pair Sum in BST, Flatten BST, Largest BST
Graphs	Shortest Path in Undirected/Weighted Graph
Arrays	Kadane's Algorithm, Count Inversions, Majority Element, Find Missing & Repeating
Strings	Implement Atoi, Validate IP Address, Smallest Distinct Window
Sliding Window	Longest Substring with K Uniques, Subarrays with Atmost K Distinct
Binary Search	Allocate Minimum Pages, Minimize Heights II, K-Sized Subarray Maximum
Math	Modular Exponentiation, Integral Points Inside Triangle, Prime Pair with Target Sum
Matrix	Left Rotate Matrix K Times, Search in Row-Column Sorted Matrix, Largest Square

📁 Path: Medium Problems

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🔴 Hard Problems

Count: 27+ problems

The most challenging problems involving advanced algorithms and complex optimizations.

Topic	Example Problems
Trees	Binary Tree to DLL, Burning Tree, Possible Paths in a Tree
DP	Edit Distance, Longest Valid Parentheses, Minimum Cost Path, Wildcard Pattern Matching
Graphs	Alien Dictionary, Maximum Connected Group
Linked Lists	Subtraction in Linked List, Clone LL with Random Pointer
Strings	Longest Prefix Suffix, Smallest Window Containing All Characters, The Palindrome Pattern
Arrays	Count Reverse Pairs, Count Smaller Elements, Median of 2 Sorted Arrays (Different Sizes)
Others	N Queen Problem, Split Array Largest Sum, Meeting Rooms III

📁 Path: Hard Problems

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Topics Covered

Data Structure / Algorithm	Difficulty Range
Arrays & Strings	School → Hard
Linked Lists (Singly, Doubly, Circular)	Basic → Hard
Stack & Queue	Basic → Medium
Binary Trees & BST	Basic → Hard
Graphs	Medium → Hard
Dynamic Programming	Medium → Hard
Greedy Algorithms	Easy → Medium
Sorting & Searching	Basic → Medium
Sliding Window & Two Pointers	Easy → Medium
Matrix Operations	School → Medium
Bit Manipulation	Easy → Medium
Math & Number Theory	School → Medium

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How to Contribute

Contributions are welcome! Follow these steps:

1. Fork & Clone

git clone https://github.com/<your-username>/GFG-Problems.git
cd GFG-Problems

2. Create a Branch

git checkout -b add/<Problem_Name>

3. Add Your Solution

• Place the file in the correct difficulty folder (School Problems/, Basic Problems/, Easy Problems/, Medium Problems/, or Hard Problems/)
• Follow the naming convention below
• Make sure your file compiles without errors

4. Verify It Compiles

g++ -std=c++17 -Wall -o test "Easy Problems/Your_Problem_Name.cpp"

5. Commit and Push

git add "Easy Problems/Your_Problem_Name.cpp"
git commit -m "Add: Your_Problem_Name (Easy)"
git push origin add/<Problem_Name>

6. Open a Pull Request

Open a PR against the main branch. Describe the problem, your approach, and the time/space complexity.

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Git Hooks Setup (Optional but Recommended)

This repository includes automatic commit message formatting via git hooks. The hooks will:

1. prepare-commit-msg — Auto-generates commit messages in the format:

   POTD DD-MM-YYYY : problem_name
   

   Example: POTD 07-07-2026 : Two Sum

2. commit-msg — Validates your commit message:

   • Ensures the message starts with POTD or a capital letter
   • Minimum 5 characters long
   • Allows merge/revert commits to bypass validation

Quick Setup

After cloning the repository, run the setup script:

bash setup-hooks.sh

Or manually set up hooks:

# Copy hooks from git_hooks/ to .git/hooks/
cp git_hooks/prepare-commit-msg .git/hooks/
cp git_hooks/commit-msg .git/hooks/

# Make them executable
chmod +x .git/hooks/prepare-commit-msg
chmod +x .git/hooks/commit-msg

Usage

Simply commit as usual — the message will be auto-generated:

git add "Easy Problems/Your_Problem_Name.cpp"
git commit
# Message auto-populates: POTD 07-07-2026 : Your_Problem_Name

Note: Git hooks are local and not pushed to GitHub. They need to be set up on each machine after cloning. The setup-hooks.sh script makes this easy!

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Naming Convention

File names follow this pattern:

Problem_Name_With_Underscores.cpp

Rules:

• Use underscores (_) instead of spaces
• Use Title_Case for each word
• Match the exact problem name from GFG as closely as possible
• .cpp extension only — do not commit .exe or compiled binaries

Examples:

✅  Kadane's_Algorithm.cpp
✅  Lowest_Common_Ancestor_in_a_BST.cpp
✅  Reverse_a_linked_list.cpp
❌  kadanes algorithm.cpp
❌  solution1.cpp
❌  Kadane's_Algorithm.exe

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License

This repository is for educational purposes. All problem statements belong to GeeksforGeeks. Solutions and code in this repository are open for learning and reference.

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