3.1 KiB
3.1 KiB
id | title | challengeType |
---|---|---|
5a23c84252665b21eecc7ee0 | Left factorials | 5 |
Description
- $!n`$
- $!n$
- $n¡$
Instructions
Tests
tests:
- text: <code>leftFactorial</code> should be a function.
testString: assert(typeof leftFactorial == 'function', '<code>leftFactorial</code> should be a function.');
- text: <code>leftFactorial(0)</code> should return a number.
testString: assert(typeof leftFactorial(0) == 'number', '<code>leftFactorial(0)</code> should return a number.');
- text: <code>leftFactorial(0)</code> should return <code>0</code>.
testString: assert.equal(leftFactorial(0), 0, '<code>leftFactorial(0)</code> should return <code>0</code>.');
- text: <code>leftFactorial(1)</code> should return <code>1</code>.
testString: assert.equal(leftFactorial(1), 1, '<code>leftFactorial(1)</code> should return <code>1</code>.');
- text: <code>leftFactorial(2)</code> should return <code>2</code>.
testString: assert.equal(leftFactorial(2), 2, '<code>leftFactorial(2)</code> should return <code>2</code>.');
- text: <code>leftFactorial(3)</code> should return <code>4</code>.
testString: assert.equal(leftFactorial(3), 4, '<code>leftFactorial(3)</code> should return <code>4</code>.');
- text: <code>leftFactorial(10)</code> should return <code>409114</code>.
testString: assert.equal(leftFactorial(10), 409114, '<code>leftFactorial(10)</code> should return <code>409114</code>.');
- text: <code>leftFactorial(17)</code> should return <code>22324392524314</code>.
testString: assert.equal(leftFactorial(17), 22324392524314, '<code>leftFactorial(17)</code> should return <code>22324392524314</code>.');
- text: <code>leftFactorial(19)</code> should return <code>6780385526348314</code>.
testString: assert.equal(leftFactorial(19), 6780385526348314, '<code>leftFactorial(19)</code> should return <code>6780385526348314</code>.');
Challenge Seed
function leftFactorial(n) {
// Good luck!
}
Solution
function leftFactorial(n) {
if (n == 0)
return 0
if (n == 1)
return 1;
// Note: for n>=20, the result may not be correct.
// This is because JavaScript uses 53 bit integers and
// for n>=20 result becomes too large.
let res = 2, fact = 2;
for (var i = 2; i < n; i++) {
res += fact;
fact *= (i + 1);
}
return res;
}