3.0 KiB
3.0 KiB
id | title | challengeType | forumTopicId |
---|---|---|---|
5eb3e4aa847216613aa81983 | Semiprime | 5 | 385318 |
Description
1679 = 23 x 73
Instructions
Tests
tests:
- text: <code>isSemiPrime</code> should be a function.
testString: assert(typeof isSemiPrime === 'function');
- text: <code>isSemiPrime(100)</code> should return a boolean.
testString: assert(typeof isSemiPrime(100) === 'boolean');
- text: <code>isSemiPrime(100)</code> should return <code>false</code>.
testString: assert.equal(isSemiPrime(100), false);
- text: <code>isSemiPrime(504)</code> should return <code>false</code>.
testString: assert.equal(isSemiPrime(504), false);
- text: <code>isSemiPrime(4)</code> should return <code>true</code>.
testString: assert.equal(isSemiPrime(4), true);
- text: <code>isSemiPrime(46)</code> should return <code>true</code>.
testString: assert.equal(isSemiPrime(46), true);
- text: <code>isSemiPrime(13)</code> should return <code>false</code>.
testString: assert.equal(isSemiPrime(13), false);
- text: <code>isSemiPrime(74)</code> should return <code>true</code>.
testString: assert.equal(isSemiPrime(74), true);
- text: <code>isSemiPrime(1679)</code> should return <code>true</code>.
testString: assert.equal(isSemiPrime(1679), true);
- text: <code>isSemiPrime(2)</code> should return <code>false</code>.
testString: assert.equal(isSemiPrime(2), false);
- text: <code>isSemiPrime(95)</code> should return <code>true</code>.
testString: assert.equal(isSemiPrime(95), true);
- text: <code>isSemiPrime(124)</code> should return <code>false</code>.
testString: assert.equal(isSemiPrime(124), false);
Challenge Seed
function isSemiPrime(n) {
}
Solution
function isSemiPrime(n) {
if (n <= 3) return false;
var ans = [];
var done = false;
while (!done) {
if (n % 2 === 0) {
ans.push(2);
n /= 2;
continue;
}
if (n % 3 === 0) {
ans.push(3);
n /= 3;
continue;
}
if (n === 1) return ans.length == 2;
var sr = Math.sqrt(n);
done = true;
// try to divide the checked number by all numbers till its square root.
for (var i = 6; i <= sr; i += 6) {
if (n % (i - 1) === 0) {
// is n divisible by i-1?
ans.push(i - 1);
n /= i - 1;
done = false;
break;
}
if (n % (i + 1) === 0) {
// is n divisible by i+1?
ans.push(i + 1);
n /= i + 1;
done = false;
break;
}
}
}
ans.push(n);
return ans.length == 2;
}