6cfd0fc503
* fix: improve Project Euler descriptions and test case Improve formatting of Project Euler test descriptions. Also add poker hands array and new test case for problem 54 * feat: add typeof tests and gave functions proper names for first 100 challenges * fix: continue fixing test descriptions and adding "before test" sections * fix: address review comments * fix: adjust grids in 18 and 67 and fix some text that reference files rather than the given arrays * fix: implement bug fixes and improvements from review * fix: remove console.log statements from seed and solution
1.8 KiB
1.8 KiB
id, challengeType, title, forumTopicId
| id | challengeType | title | forumTopicId |
|---|---|---|---|
| 5900f3801000cf542c50fe93 | 5 | Problem 20: Factorial digit sum | 301839 |
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!
Instructions
Tests
tests:
- text: <code>sumFactorialDigits(10)</code> should return a number.
testString: assert(typeof sumFactorialDigits(10) === 'number');
- text: <code>sumFactorialDigits(10)</code> should return 27.
testString: assert.strictEqual(sumFactorialDigits(10), 27);
- text: <code>sumFactorialDigits(25)</code> should return 72.
testString: assert.strictEqual(sumFactorialDigits(25), 72);
- text: <code>sumFactorialDigits(50)</code> should return 216.
testString: assert.strictEqual(sumFactorialDigits(50), 216);
- text: <code>sumFactorialDigits(75)</code> should return 432.
testString: assert.strictEqual(sumFactorialDigits(75), 432);
- text: <code>sumFactorialDigits(100)</code> should return 648.
testString: assert.strictEqual(sumFactorialDigits(100), 648);
Challenge Seed
function sumFactorialDigits(n) {
// Good luck!
return n;
}
sumFactorialDigits(100);
Solution
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));
}