🧮 JavaScript Algorithms

Classic data structures and algorithms, implemented in clean, modern JavaScript - each one documented, complexity-annotated, and covered by tests.

A study-and-reference collection of well-known algorithms and data structures. Every module is a small, self-contained ES module with:

• 📖 a docstring explaining the idea and its time/space complexity,
• 🧩 clear, commented code that favors readability over cleverness,
• ✅ a matching Vitest test that doubles as usage examples.

Great for interview prep, brushing up on fundamentals, or as a base to contribute your own.

🚀 Getting started

git clone https://github.com/rope-50/javascript-algorithms.git
cd javascript-algorithms
npm install

npm test          # run the whole suite once
npm run test:watch  # re-run on file changes
npm run coverage    # run with a coverage report

Requires Node.js 20+.

📦 Usage

Everything is exported from src/, individually or via the barrel src/index.js:

import { mergeSort, BinarySearchTree, runningMedian } from './src/index.js';

mergeSort([5, 2, 9, 1]);            // -> [1, 2, 5, 9]

new BinarySearchTree()
  .insertAll([5, 3, 8, 1])
  .inOrder();                       // -> [1, 3, 5, 8]

runningMedian([12, 4, 5, 3]);       // -> [12, 8, 5, 4.5]

📚 What's inside

Data structures

Structure	Source	Highlights
Binary heap (min/max)	heap.js	push/pop O(log n), custom comparator
Queue (two stacks)	queue.js	FIFO with O(1) amortized ops
Binary search tree	binarySearchTree.js	insert / delete / search / traversals
Trie (prefix tree)	trie.js	word lookup + prefix counting

Sorting & counting

Algorithm	Source	Complexity
Merge sort	mergeSort.js	O(n log n)
Count inversions	mergeSort.js	O(n log n)
Running median	runningMedian.js	O(log n) / element

Math

Algorithm	Source	Complexity
Factorial	factorial.js	O(n)
Primality test	primes.js	O(√n)
Sieve of Eratosthenes	primes.js	O(n log log n)
Polynomial derivative & integral	polynomial.js	O(n)

Strings

Algorithm	Source	Complexity
Reverse string	reverseString.js	O(n)
Permutation check	stringPermutation.js	O(n)
Ransom note	ransomNote.js	O(n)

Classic problems

Problem	Source	Complexity
Coin change (count ways)	coinChange.js	O(amount × coins)
H-index	hIndex.js	O(n)
Celebrity problem	celebrity.js	O(n)
Permutations	permutations.js	O(n · n!)

🗂️ Project structure

src/      one module per algorithm or data structure
tests/    one Vitest spec per module (mirrors src/)

🤝 Contributing

Contributions are very welcome - whether it's a brand-new algorithm, a clearer explanation, an extra test, or a bug fix. New to open source? This is a friendly place to make your first PR. 💚

Have a look at CONTRIBUTING.md for the (short) guidelines, then open an issue or a pull request. Every addition just needs a docstring with its complexity and a test.

📄 License

Released under the MIT License.