mathball/lib/catalan/index.js

A JavaScript library for Competitive Programming

'use strict';

/* Nth Catalan Number
 * Function: catalan()
 */

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

function binomialCoeff(n, k) {
	var res = 1;
	for (var i = 0; i < k; i++) {
		res = res * (n - i);
		res = res / (i + 1);
	}
	return res;
}

exports.find = function (num) {
	validate(num, 'catalan');
	var c = binomialCoeff(2 * num, num);
	return c / (num + 1);
};