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// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.// This module is browser compatible.
/** * Builds all possible orders of all elements in the given array * Ignores equality of elements, meaning this will always return the same * number of permutations for a given length of input. * * Example: * * ```ts * import { permutations } from "https://deno.land/std@$STD_VERSION/collections/mod.ts"; * import { assertEquals } from "https://deno.land/std@$STD_VERSION/testing/asserts.ts"; * * const numbers = [ 1, 2 ] * const windows = permutations(numbers) * * assertEquals(windows, [ * [ 1, 2 ], * [ 2, 1 ], * ]) * ``` */export function permutations<T>(inputArray: readonly T[]): T[][] { const ret: T[][] = []; const k = inputArray.length;
if (k === 0) { return ret; }
// Heap's Algorithm const array = [...inputArray]; const c = new Array<number>(k).fill(0);
ret.push([...array]);
let i = 1;
while (i < k) { if (c[i] < i) { if (i % 2 === 0) { [array[0], array[i]] = [array[i], array[0]]; } else { [array[c[i]], array[i]] = [array[i], array[c[i]]]; }
ret.push([...array]);
c[i] += 1; i = 1; } else { c[i] = 0; i += 1; } }
return ret;}