# atcoder/ac-library

AtCoder Library

Repository: https://github.com/atcoder/ac-library
Canonical: https://ross.abutalabs.com/products/ac-library
Language: C++
License: CC0-1.0
License Family: permissive
Topics: atcoder, atcoder-library, competitive-programming
Last push: 2025-05-01T16:53:01+00:00

## Health v2 (maintenance only)
Score: 31/100 (v2, computed 2026-09-02T17:46:02.011165+00:00)
- activity 19, release rhythm 8, longevity 100
- inputs: {"age_days": 2185, "days_push": 489, "days_rel": 489, "gap_med": null, "n_releases_24m": 1}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 2345, forks 268 (observed 2026-08-28T04:06:39.827272+00:00)

## What it is
The official C++ library for AtCoder, providing well-tested implementations of common algorithms and data structures used in competitive programming. It is designed for minimal learning effort and maximum contest convenience, intentionally ignoring general-purpose C++ conventions.

## Use cases
- use segment trees and Fenwick trees in competitive programming contests
- compute max flow and min cost flow quickly during a contest
- use modular arithmetic and convolution helpers for math problems
- get a ready-made DSU (union-find) implementation for AtCoder problems
- avoid rewriting standard competitive programming algorithms in C++

## When to choose
- you compete on AtCoder (or similar judges) in C++ and want reliable, fast standard algorithms
- you want a CC0-licensed, header-only library with zero setup effort
- you need contest-focused implementations that prioritize simplicity over generality

## When to avoid
- you need a general-purpose production C++ library with idiomatic APIs (it intentionally ignores C++ conventions)
- you need features beyond the fixed algorithm set, since new features are not being added
- you work in a language other than C++

## Facets
- artifact type: library
- maturity: maintenance
- function: math
- domain: -
- platform: cpp, cross-platform
- tags: atcoder, competitive-programming, header-only, algorithms, data-structures, cpp

## Member repositories
- atcoder/ac-library (main) score 31

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:06:39.827272+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T02:37:02.711179+00:00, confidence not recorded.
  - readme: https://github.com/atcoder/ac-library (fetched 2026-08-28T04:06:39.827272+00:00, sha c9f4eda1d9f4)
- Data as of 2026-08-30T08:39:29.467469+00:00.