# martinus/robin-hood-hashing

Fast & memory efficient hashtable based on robin hood hashing for C++11/14/17/20

Repository: https://github.com/martinus/robin-hood-hashing
Canonical: https://ross.abutalabs.com/products/robin-hood-hashing
Homepage: https://gitter.im/martinus/robin-hood-hashing
Language: C++
License: MIT
License Family: permissive
Topics: c-plus-plus, hash-tables, unordered-maps, hash, container, header-only, stl-containers, single-file, no-dependencies, cpp, cpp14, cpp11
Archived: true
Last push: 2023-05-01T21:43:58+00:00

## Health v2 (maintenance only)
Score: 10/100 (v2, computed 2026-09-03T02:20:16.233290+00:00)
- activity 0, release rhythm 8, longevity 100
- inputs: {"age_days": 4785, "days_push": 1220, "days_rel": null, "gap_med": null, "n_releases_24m": 0}
- flags: archived
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 1621, forks 153 (observed 2026-08-28T04:05:12.487404+00:00)

## What it is
A header-only C++ library providing robin_hood::unordered_map and robin_hood::unordered_set as fast, memory-efficient drop-in replacements for std::unordered_map and std::unordered_set. It is based on robin hood hashing and supports C++11/14/17/20 with no dependencies.

## Use cases
- replace std::unordered_map with a faster hashmap
- reduce memory usage of hash tables in C++
- speed up lookups in performance-critical C++ code
- drop-in single-file hashmap for C++11 through C++20
- use a fast unordered_set without dependencies

## When to avoid
- you want active development or new features - the author recommends the successor ankerl::unordered_dense
- you need non-standard hash table features beyond map/set semantics

## Facets
- artifact type: library
- maturity: maintenance
- function: caching, developer-tools
- domain: performance, developer-tools
- platform: cpp, cross-platform
- tags: hash-table, robin-hood-hashing, header-only, unordered-map, unordered-set, stl-replacement, single-file, no-dependencies, algorithms

## Member repositories
- martinus/robin-hood-hashing (main) score 10

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:05:12.487404+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 2026-08-30T03:49:14.822732+00:00, confidence not recorded.
  - readme: https://github.com/martinus/robin-hood-hashing (fetched 2026-08-28T04:05:12.487404+00:00, sha 187968e3dd6e)
- Data as of 2026-08-30T08:39:29.467469+00:00.