Coding Problems

Here you can find solutions for various coding/algorithmic problems and many useful resources for learning algorithms and data structures.
Also, this repo will be updated with new solutions and resources from time to time.

Note that this repo is meant to be used for learning and researching purposes only and it is not meant to be used for production.

Solutions

Algorithms and data structures are not language-specific (it's true that some languages are faster, and some are easier to use), but if you are good with the logic and pseudocode, any language would be good.
So I've decided to use C++/C
So, to execute these solutions there is no need from installing any external packages. Most of the links to the respective questions are either added in the code as comment or as a commit message

Note that I'm not the author of these problems, they are from sites like LeetCode (you can find more than 40 sites like this in the Training Sites section). Only the solutions and explanations are mine. If you find any bug or incorrect implementation (or faster/better implementation) in this repo, please let me know by opening an issue or pull request.

Categories

Each solution/problem in this repo belongs to one of these categories:

1. Graph -DFS,BFS, Shortes Paths, Cycles,Euler Tour, Spanning Trees, Bipartite Graphs, Strongly Connected Components, Topological Sorting etc.
2. Dynamic Programming - 3D, 2D and 1D Dynamic Programming, LCS, LIS, Knapsack, MCM, DP on Tress , DP on Strings etc.
3. Segment Tree Implementation, Range Query.
4. Trie Implementation, Unique Prefix Array, Max Xor Pairs.
5. Arrays - Array Manipulations, Sorting, Prefix Sum, Sliding Window, etc.
6. Linked Lists - Linked List Searching, Pointer Manipulations, etc.
7. Trees - Binary Search Trees, Tree Traversals: Breadth-First (Level Order) Traversal, Depth-First Traversal (Inorder, Preorder, Postorder),Successors, Forest, Sum Tress, LCA etc.
8. Recursion and Backtracking - Permutations,Combinations, Sudoku Solver, N-Queens
9. Math - Combinatorics, Prime,GCD, LCM, Factorization, Geometry, Math Formulas, etc.
10. Binary Search
11. Sorting Bubble, Insertion,Merge, Quick Sort etc.
12. Heap
13. HashTable
14. Stacks
15. Greedy
16. Euler Project Solution
17. Bitwise Operations
18. Other -Arrays, Matrices,Searching ,Sorting, String.

Learning Resources

The learning resources are divided into 4 categories: Courses, Books, Training Sites, Other Resources.

Courses

Collection of free courses from one of the best CS universities.

1. Stanford University

   • Algorithms Specialization (Coursera)
     • Divide and Conquer, Sorting and Searching, and Randomized Algorithms
     • Graph Search, Shortest Paths, and Data Structures
     • Greedy Algorithms, Minimum Spanning Trees, and Dynamic Programming
     • Shortest Paths Revisited, NP-Complete Problems and What To Do About Them
   • Introduction to Programming Contests - CS 97SI

2. Princeton University

   • Algorithms Part 1 (Coursera)
   • Algorithms Part 2 (Coursera)
   • Analysis of Algorithms (Coursera)

3. UC San Diego

   • Data Structures and Algorithms Specialization (Coursera)
     • Algorithmic Toolbox
     • Data Structures
     • Algorithms on Graphs
     • Algorithms on Strings
     • Advanced Algorithms and Complexity
   • Data Structures and Performance (Coursera)
   • edX
     • Data Structures Fundamentals
     • Algorithmic Design and Techniques
     • Graph Algorithms
     • Data Structures: An Active Learning Approach

4. MIT University

   • Introduction to algorithms 2005 - Official MIT page with resources. Note: this course is the old 6.046J course (the new name is Design and analysis of algorithms, you can find it below).
   • Introduction to algorithms 2011 - 6.006 - Official MIT page with resources
   • Design and analysis of algorithms - 6.046J - Official MIT page with resources
   • Advanced Data Structures - 6.851 - Official MIT page with resources
   • Advanced Algorithms 2016 - 6.854 - Official MIT page with resources

5. Harvard University

   • Advanced algorithms - CS224

6. UC Berkeley

   • Data Structures - CS61B
   • Efficient Algorithms and Intractable Problems - CS170 - YouTube videos

Books

Several books that have made an impression on me:

1. Grokking Algorithms by Aditya Bhargava - The best book for complete beginners in algorithms! I wish this book existed when I started learning algorithms.
2. Introduction to Algorithms by CLRS - This book is called the "bible textbook of algorithms" by many programmers.
3. Algorithms by Robert Sedgewick & Kevin Wayne - These authors are instructors of the previously mentioned Coursera courses: Algorithms Part 1 and Algorithms Part 2. Also, this book has an excellent and free site with exercises, presentations, and examples.
4. The Algorithm Design Manual by Steven Skiena - The book describes many advanced topics and algorithms and it focuses on real-life practical examples. This book has one of the best sites with resources (solutions, algorithms and data structures, python implementations).
5. Algorithms by S. Dasgupta, C. Papadimitriou, and U. Vazirani - This book is an official book for algorithms and data structures classes in several famous universities.
6. Competitive Programming 3 by Steven Halim & Felix Halim - A great book that prepares you for competitive programming (not for complete beginners). You can learn many things and tricks about competitive programming. But if your goal is to prepare for competitive programming then choose a faster language than Python, C/C++ (or Java, it's faster than Python but not like C/C++).
7. Cracking the Coding Interview by Gayle Laakmann McDowell - A bit different from the previous books. Prepares you for coding interviews using great coding problems.

Training Sites

If the problems from LeetCode are not enough and you need more problems like those, you can find much more on these platforms:

• HackerRank
• CodeChef
• HackerEarth
• CodeForces
• Topcoder
• Project Euler
• SPOJ
• A2OJ
• PEG
• Online Judge
• E-Olymp
• VJudge
• DMOJ
• USA CO
• Rosetta Code
• AtCoder
• Russian Code Cup
• LintCode
• Kattis
• CodeAbbey
• CS Academy
• Advent of Code
• Exercism
• CodeFu
• Mendo
• Z-Training
• Codewars
• Wolfram Challenges
• Google's Coding Competitions
• Cyber-dojo
• CodingBat
• CodeKata
• BinarySearch
• Daily Coding Problem
• Daily Interview Pro
• AlgoDaily
• Codility
• CoderByte
• AlgoExpert
• CodeSignal
• Edabit
• DevPost
• Brilliant
• Codingame
• CheckiO
• FightCode
• Kaggle
• Rosalind

Other Resources

1. Geeks For Geeks - The site which all interested in algorithms (no matter if beginners or experts) should know! YouTube channel with many useful videos.
2. The Algorithms - Python - Great GitHub repo with many algorithms written in Python (Link from the same repo written in other programming languages).
3. CP Algorithms - Great page with excellent explanations for various algorithms.
4. Visualizers:
   • USFCA Visualization Tool - Great tool for visualizing data structures and algorithms, created by the University of San Francisco.
   • VisuAlgo - Another great tool for visualizing data structures and algorithms through animation.
   • Algorithm Visualizer - Interactive online platform that visualizes algorithms from code. This platform is an open-source project, here you can find the source code.
5. Courses and tutorials (but not from universities like the Courses section):
   • Google - Intro to Data Structures and Algorithms - Free course on Udacity offered by Google.
   • Microsoft - Algorithms and Data Structures - Free course on edX offered by Microsoft.
   • HackerEarth - Tutorials and Practice - Practice problems and learn about many algorithms and data structures needed for competitive programming.
   • KhanAcademy - Algorithms - Good explanations for some basic algorithms.
   • Tutorialspoint - Data Structures and Algorithms - Another platform with good explanations, also Tutorialspoint has free tutorials for almost everything related to CS!
   • Programiz - Data Structures and Algorithms - One more platform which explains the data structures and algorithms in a simple and interesting way.
   • Hackr.io - Data Structures and Algorithms Tutorials and Courses - Big collection of tutorials and courses.
   • Classpert - Data Structures and Algorithms Courses - List of over 80 Online Courses (free and paid).
6. YouTube playlists with tutorials:
   • Data Structures by mycodeschool
   • Data Structures by HackerRank
   • Algorithms by HackerRank