locutus/haskell/list/permutations.js

Locutus other languages' standard libraries to JavaScript for fun and educational purposes

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.permutations = permutations;
function permutationsInternal(items) {
    if (items.length === 0) {
        return [[]];
    }
    const out = [];
    for (let i = 0; i < items.length; i++) {
        const current = items[i];
        const rest = items.slice(0, i).concat(items.slice(i + 1));
        for (const tail of permutationsInternal(rest)) {
            out.push([current, ...tail]);
        }
    }
    return out;
}
function permutations(items) {
    //  discuss at: https://locutus.io/haskell/list/permutations/
    // original by: Kevin van Zonneveld (https://kvz.io)
    //      note 1: Returns all permutations, preserving Haskell's empty-list behavior (one empty permutation).
    //   example 1: permutations([1, 2, 3])
    //   returns 1: [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]
    //   example 2: permutations(['a', 'b'])
    //   returns 2: [['a', 'b'], ['b', 'a']]
    //   example 3: permutations([])
    //   returns 3: [[]]
    if (!Array.isArray(items)) {
        return [[]];
    }
    return permutationsInternal(items.slice());
}