Function factorial

project_euler_problems/lattice paths/solution.js:12–23

(n)

 */

function factorial(n) {
	if (n === 0 || n === 1) {
		return 1;
	}

	let sum = 1;
	for (let i = 2; i <= n; i++) {
		sum = sum * i;
	}

	return sum;
}

function countPaths(gridSize) {
	return Math.floor(factorial(gridSize * 2) / Math.pow(factorial(gridSize), 2));