The Sorting Algorithms Library

Everything about sorting, properly explained

42 guides that answer the questions people actually ask — from what a sorting algorithm is, through complexity and cache behaviour, to what your language runs under the hood. Written for beginners, detailed enough for interviews.

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New to sorting? Read these three.

Fundamentals What Is a Sorting Algorithm? The plain-English definition of a sorting algorithm, why ordered data is so valuable, and where you already rely on sorting every day. 6 min read Reference & Cheatsheets Sorting Algorithms Big O Cheat Sheet One table with every algorithm's best, average and worst case, space cost and stability — plus how to actually read it and a trick for memorising the lot. 9 min read Reference & Cheatsheets Which Sorting Algorithm Should I Use? Stop memorising and start deciding. Six questions about your data that lead to the right algorithm — plus when the correct answer is just to use the built-in sort. 10 min read
8 guides

Fundamentals

What Is a Sorting Algorithm? The plain-English definition of a sorting algorithm, why ordered data is so valuable, and where you already rely on sorting every day. 6 min read Read guide How Do Sorting Algorithms Work? Every sorting algorithm is built from a small set of operations: compare, swap, insert, and merge. Here is how they combine. 7 min read Read guide Comparison vs Non-Comparison Sorting Why comparison sorts can never beat O(n log n) — and how Counting and Radix Sort sidestep that limit to reach linear time. 6 min read Read guide Time Complexity of Sorting Algorithms: The Big O Cheat Sheet The complete best/average/worst-case Big O table for every major sorting algorithm, with notes on space and stability. 10 min read Read guide Space Complexity in Sorting Algorithms Time is not the only cost. Here is how much extra memory each sorting algorithm needs and why it matters. 8 min read Read guide Stable vs Unstable Sorting Algorithms What stability means, why it is essential for multi-key sorting, and a clear list of which algorithms are stable. 6 min read Read guide What Are Adaptive Sorting Algorithms? Why some algorithms speed up when the data is already partly ordered — and how Tim Sort turns that into its superpower. 7 min read Read guide Why Is O(n log n) the Lower Bound for Comparison Sorting? The elegant decision-tree argument that proves no comparison-based sort can ever beat O(n log n). 6 min read Read guide
3 guides

Reference & Cheatsheets

Sorting Algorithms Big O Cheat Sheet One table with every algorithm's best, average and worst case, space cost and stability — plus how to actually read it and a trick for memorising the lot. 9 min read Read guide Types of Sorting Algorithms Every major sorting algorithm in one place, grouped into the four families they belong to — so twelve separate things become four ideas with variations. 12 min read Read guide Which Sorting Algorithm Should I Use? Stop memorising and start deciding. Six questions about your data that lead to the right algorithm — plus when the correct answer is just to use the built-in sort. 10 min read Read guide
12 guides

Algorithm Deep Dives

Bubble Sort Explained The classic teaching algorithm: how Bubble Sort works, why it is O(n²), and the one optimization that makes it adaptive. 6 min read Read guide Selection Sort Explained The algorithm that makes the fewest swaps: how Selection Sort works and when its minimal-write property is useful. 5 min read Read guide Insertion Sort Explained The card-player's algorithm: how Insertion Sort works, why it is adaptive, and why fast sorts switch to it for small arrays. 6 min read Read guide Merge Sort Explained The reliable divide-and-conquer sort: guaranteed O(n log n), stable, and the basis for external sorting of huge datasets. 7 min read Read guide Quick Sort Explained The fastest practical sort: how partitioning works, why pivot choice is everything, and how to avoid the O(n²) trap. 7 min read Read guide Heap Sort Explained The only comparison sort that is both O(n log n) guaranteed and in-place — how Heap Sort uses a binary heap to do it. 6 min read Read guide Shell Sort Explained How Shell Sort supercharges Insertion Sort with gap sequences, and why the gap choice determines its performance. 5 min read Read guide Counting Sort Explained How Counting Sort breaks the O(n log n) barrier for bounded integers — and the memory cost that limits where you can use it. 5 min read Read guide Radix Sort Explained How Radix Sort sorts huge integer arrays in linear-ish time by processing one digit at a time with a stable sub-sort. 6 min read Read guide Tim Sort Explained Why the world's most-used sort is a hybrid: how Tim Sort detects natural runs and merges them for blazing real-world speed. 7 min read Read guide Bucket Sort Explained How Bucket Sort achieves linear average time on uniformly distributed data by scattering elements into buckets. 5 min read Read guide Introsort Explained How Introsort blends Quick, Heap, and Insertion Sort to get Quick Sort's speed without its O(n²) worst case. 6 min read Read guide
6 guides

Comparisons

Quick Sort vs Merge Sort The most-asked sorting question on the internet, settled: speed, memory, stability, and worst-case, point by point. 10 min read Read guide Quick Sort vs Heap Sort vs Merge Sort All three run in O(n log n), yet they behave completely differently in practice. How Quick Sort, Heap Sort and Merge Sort trade speed against memory and stability. 9 min read Read guide Bubble Sort vs Insertion Sort vs Selection Sort The three beginner sorts are all quadratic, yet they are not equivalent. Which one actually wins, why Selection Sort survives despite losing, and when any of them is right. 8 min read Read guide Quick Sort vs Tim Sort Quick Sort is faster on random data, so why do modern languages default to Tim Sort? Stability and real-world inputs. 8 min read Read guide Counting Sort vs Radix Sort Two linear-time integer sorts compared — and why Radix Sort exists to fix Counting Sort's memory problem. 8 min read Read guide Which Sorting Algorithm Is Fastest? “Fastest” depends entirely on your data. A decision guide for nearly-sorted input, small arrays, datasets too big for memory, and integer keys. 11 min read Read guide
5 guides

Systems & Performance

Sorting Algorithms in the Real World The algorithms that actually run when you call sort() — in Python, Java, C++, V8, PostgreSQL and on GPUs — and the engineering reason behind each choice. 11 min read Read guide Why Quick Sort Is Faster in Practice Two algorithms, identical Big O, one is three times faster. The answer is CPU cache — and it is the most useful thing Big O deliberately hides from you. 10 min read Read guide Quick Sort Pivot Selection Strategies Quick Sort's entire reputation rests on one line of code: how it picks the pivot. Here is every strategy, what breaks it, and what real libraries do. 10 min read Read guide External Sorting Explained Sorting 500 GB on a machine with 8 GB of RAM. How external merge sort works, why sequential I/O changes everything, and where you already rely on it. 11 min read Read guide In-Place vs Out-of-Place Sorting Sorting inside the original array versus building a new one — what "in-place" actually means, why recursion still counts, and what the choice costs you. 9 min read Read guide
4 guides

Language Implementations

Sorting Algorithms in Python Clean Python implementations of the core sorts, plus how the built-in sorted() and list.sort() actually work. 10 min read Read guide Sorting Algorithms in Java Java sort implementations plus the surprising reason Arrays.sort uses two different algorithms for objects and primitives. 10 min read Read guide Sorting Algorithms in JavaScript JS sort implementations, the infamous Array.sort numeric gotcha, and how V8 uses Tim Sort under the hood. 10 min read Read guide Sorting Algorithms in C++ C++ sort implementations plus a tour of std::sort, std::stable_sort, and the Introsort engine behind them. 10 min read Read guide
2 guides

Interview & Career

Sorting Algorithms for Coding Interviews What interviewers actually test when they ask about sorting, what is worth memorising versus understanding, and the problem patterns where sorting is the hidden first step. 11 min read Read guide Top Sorting Algorithm Interview Questions and Answers The questions that come up again and again, with crisp answers you can adapt in your own words. 10 min read Read guide
2 guides

Learning & Tools

How to Use a Sorting Visualizer to Learn Faster A practical, repeatable study method for turning a sorting visualizer into deep understanding. 8 min read Read guide Why Learn Sorting Algorithms? If the standard library already sorts, why learn the algorithms? Because they teach the skills everything else builds on. 8 min read Read guide

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