1.4 KiB
1.4 KiB
id | title | challengeType | forumTopicId | dashedName |
---|---|---|---|---|
5900f3801000cf542c50fe93 | Problem 20: Factorial digit sum | 5 | 301839 | problem-20-factorial-digit-sum |
--description--
n
! means n
× (n
− 1) × ... × 3 × 2 × 1
For example, 10! = 10 × 9 × ... × 3 × 2 × 1 = 3628800,
and the sum of the digits in the number 10! is 3 + 6 + 2 + 8 + 8 + 0 + 0 = 27.
Find the sum of the digits n
!
--hints--
sumFactorialDigits(10)
should return a number.
assert(typeof sumFactorialDigits(10) === 'number');
sumFactorialDigits(10)
should return 27.
assert.strictEqual(sumFactorialDigits(10), 27);
sumFactorialDigits(25)
should return 72.
assert.strictEqual(sumFactorialDigits(25), 72);
sumFactorialDigits(50)
should return 216.
assert.strictEqual(sumFactorialDigits(50), 216);
sumFactorialDigits(75)
should return 432.
assert.strictEqual(sumFactorialDigits(75), 432);
sumFactorialDigits(100)
should return 648.
assert.strictEqual(sumFactorialDigits(100), 648);
--seed--
--seed-contents--
function sumFactorialDigits(n) {
return n;
}
sumFactorialDigits(100);
--solutions--
let factorial = (n) => n <= 1 ? BigInt(n) : BigInt(n) * BigInt(factorial(--n));
let sumDigits = n => n.toString().split('').map(x => parseInt(x)).reduce((a,b) => a + b);
function sumFactorialDigits(n) {
return sumDigits(factorial(n));
}