diff --git a/package.json b/package.json index 80cbfff..2c05cd2 100644 --- a/package.json +++ b/package.json @@ -1,7 +1,7 @@ { "name": "@combinatorics/n-permutations", "description": "Set n-permutations for JavaScript", - "version": "0.0.1", + "version": "0.1.0", "license": "AGPL-3.0", "author": "make-github-pseudonymous-again", "homepage": "https://computational-combinatorics.github.io/n-permutations", diff --git a/src/_permutations.js b/src/_permutations.js new file mode 100644 index 0000000..25db354 --- /dev/null +++ b/src/_permutations.js @@ -0,0 +1,51 @@ +import assert from 'assert'; +import {_take} from '@iterable-iterator/slice'; + +import {list} from '@iterable-iterator/list'; +import { + forwardRangeIterator, + backwardRangeIterator, +} from '@iterable-iterator/range'; + +/** + * Yields all k-permutations of {0, 1, ..., n-1}. + * + * @param {number} n + * @param {number} k + * @returns {IterableIterator>} + */ +export default function* _permutations(n, k) { + assert(Number.isInteger(k) && k >= 0); + if (k > n) return; + + const indices = list(forwardRangeIterator(0, n, 1)); + const cycles = list(backwardRangeIterator(n, n - k, -1)); + + yield _take(indices, k); + + if (k === 0 || n === 0) return; + + while (true) { + let i = k; + + while (i--) { + --cycles[i]; + + if (cycles[i] === 0) { + // Could be costly + indices.push(indices.splice(i, 1)[0]); + + cycles[i] = n - i; + } else { + const j = cycles[i]; + + [indices[i], indices[n - j]] = [indices[n - j], indices[i]]; + + yield _take(indices, k); + break; + } + } + + if (i === -1) return; + } +} diff --git a/src/index.js b/src/index.js index 6dd94d7..6e892ad 100644 --- a/src/index.js +++ b/src/index.js @@ -1 +1,2 @@ +export {default as _permutations} from './_permutations.js'; export {default as permutations} from './permutations.js'; diff --git a/src/permutations.js b/src/permutations.js index c65e54c..70d2921 100644 --- a/src/permutations.js +++ b/src/permutations.js @@ -1,9 +1,7 @@ -import assert from 'assert'; -import {_take} from '@iterable-iterator/slice'; - import {list} from '@iterable-iterator/list'; -import {pick} from '@iterable-iterator/map'; -import {range} from '@iterable-iterator/range'; +import {map, pick} from '@iterable-iterator/map'; + +import _permutations from './_permutations.js'; /** * Yields all permutations of each possible choice of r elements @@ -21,48 +19,12 @@ import {range} from '@iterable-iterator/range'; * @param {number} r - The size of the permutations to generate. * @returns {IterableIterator} */ -export default function* permutations(iterable, r) { - assert(Number.isInteger(r) && r >= 0); +const permutations = (iterable, r) => { const pool = list(iterable); + return map( + (indices) => list(pick(pool, indices)), + _permutations(pool.length, r), + ); +}; - const length = pool.length; - - if (r > length) { - return; - } - - const indices = list(range(0, length, 1)); - const cycles = list(range(length, length - r, -1)); - - yield list(pick(pool, _take(indices, r))); - - if (r === 0 || length === 0) { - return; - } - - while (true) { - let i = r; - - while (i--) { - --cycles[i]; - - if (cycles[i] === 0) { - // Could be costly - indices.push(indices.splice(i, 1)[0]); - - cycles[i] = length - i; - } else { - const j = cycles[i]; - - [indices[i], indices[length - j]] = [indices[length - j], indices[i]]; - - yield list(pick(pool, _take(indices, r))); - break; - } - } - - if (i === -1) { - return; - } - } -} +export default permutations; pFad - Phonifier reborn

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