mathball/lib/ncr/index.js

A JavaScript library for Competitive Programming

'use strict';

/* nCr
 * Function: nCr()
 */

var validate = require('../validation/non-negative-integer');

/**
 *
 * @param {number, number} number
 * @returns {number}
 */

function nCr(number1, number2) {

	var res = 1;
	var i = 0;
	if (number2 > number1 - number2) {
		number2 = number1 - number2;
	}
	for (; i < number2; ++i) {
		res *= number1 - i;
		res /= i + 1;
	}
	return res;
}

exports.nCr = function (number1, number2) {
	validate(number1, 'nCr');
	validate(number2, 'nCr');
	if (number1 < number2) {
		throw new TypeError('n >= r condition not satisfied.\n');
	}
	return nCr(number1, number2);
};