--description--

Given an integer from zero to 20, return the factorial of that number. The factorial of a number is the product of all the numbers between 1 and the given number.

• The factorial of zero is 1.

--hints--

factorial(0) should return 1.

assert.equal(factorial(0), 1);

factorial(5) should return 120.

assert.equal(factorial(5), 120);

factorial(20) should return 2432902008176640000.

assert.equal(factorial(20), 2432902008176640000);

--seed--

--seed-contents--

function factorial(n) {

  return n;
}

--solutions--

function factorial(n) {
  return n == 0 ? 1 : n * factorial(n - 1);
}