mathjs/lib/esm/function/probability/permutations.js

import { isInteger } from '../../utils/number.js';
import { product } from '../../utils/product.js';
import { factory } from '../../utils/factory.js';
var name = 'permutations';
var dependencies = ['typed', 'factorial'];
export var createPermutations = /* #__PURE__ */factory(name, dependencies, (_ref) => {
  var {
    typed,
    factorial
  } = _ref;

  /**
   * Compute the number of ways of obtaining an ordered subset of `k` elements
   * from a set of `n` elements.
   *
   * Permutations only takes integer arguments.
   * The following condition must be enforced: k <= n.
   *
   * Syntax:
   *
   *     math.permutations(n)
   *     math.permutations(n, k)
   *
   * Examples:
   *
   *    math.permutations(5)     // 120
   *    math.permutations(5, 3)  // 60
   *
   * See also:
   *
   *    combinations, combinationsWithRep, factorial
   *
   * @param {number | BigNumber} n   The number of objects in total
   * @param {number | BigNumber} [k] The number of objects in the subset
   * @return {number | BigNumber}    The number of permutations
   */
  return typed(name, {
    'number | BigNumber': factorial,
    'number, number': function numberNumber(n, k) {
      if (!isInteger(n) || n < 0) {
        throw new TypeError('Positive integer value expected in function permutations');
      }

      if (!isInteger(k) || k < 0) {
        throw new TypeError('Positive integer value expected in function permutations');
      }

      if (k > n) {
        throw new TypeError('second argument k must be less than or equal to first argument n');
      } // Permute n objects, k at a time


      return product(n - k + 1, n);
    },
    'BigNumber, BigNumber': function BigNumberBigNumber(n, k) {
      var result, i;

      if (!isPositiveInteger(n) || !isPositiveInteger(k)) {
        throw new TypeError('Positive integer value expected in function permutations');
      }

      if (k.gt(n)) {
        throw new TypeError('second argument k must be less than or equal to first argument n');
      }

      var one = n.mul(0).add(1);
      result = one;

      for (i = n.minus(k).plus(1); i.lte(n); i = i.plus(1)) {
        result = result.times(i);
      }

      return result;
    } // TODO: implement support for collection in permutations

  });
});
/**
 * Test whether BigNumber n is a positive integer
 * @param {BigNumber} n
 * @returns {boolean} isPositiveInteger
 */

function isPositiveInteger(n) {
  return n.isInteger() && n.gte(0);
}