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// This module is browser compatible.
/** * Yields `r` length `Arrays` from the input `iterable`. Order of selection is * important and elements are chosen without replacement. If `r` is undefined, then * the length of the `iterable` is used. * * ```ts * import { assertEquals } from "https://deno.land/std/testing/asserts.ts"; * import { permutations } from "https://deno.land/x/combinatorics/mod.ts"; * * const sequences = [...permutations([1, 2, 3, 4], 2)]; * * assertEquals(sequences, [ *   [1, 2], [1, 3], [1, 4], *   [2, 1], [2, 3], [2, 4], *   [3, 1], [3, 2], [3, 4], *   [4, 1], [4, 2], [4, 3], * ]); * ``` */export function* permutations<T>(  iterable: Iterable<T>,  r?: number,): Generator<T[]> {  const pool = [...iterable];  const n = pool.length;  if (r === undefined) {    r = n;  } else if (!Number.isInteger(r) || r < 0) {    throw RangeError("r must be a non-negative integer");  } else if (r > n) {    return;  }  const cycles = Array(r).fill(0).map((_, index) => n - index);  const indices = new Uint32Array(n).map((_, index) => index);  yield pool.slice(0, r);  while (true) {    loop: {      for (let i = r - 1; i >= 0; i--) {        cycles[i] -= 1;        if (cycles[i] === 0) {          let index = indices[i];          for (let j = n - 1; j >= i; j--) {            const temp = index;            index = indices[j];            indices[j] = temp;          }          cycles[i] = n - i;        } else {          const j = n - cycles[i];          const temp = indices[i];          indices[i] = indices[j];          indices[j] = temp;          const result = Array(r);          for (i = 0; i < r; i++) {            result[i] = pool[indices[i]];          }          yield result;          break loop;        }      }      return;    }  }}