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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@$STD_VERSION/collections/permutations.ts"; * import { assertEquals } from "https://deno.land/std@$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;}