147 lines
2.4 KiB
Markdown
147 lines
2.4 KiB
Markdown
---
|
|
id: 5eb3e4aa847216613aa81983
|
|
title: Semiprime
|
|
challengeType: 5
|
|
forumTopicId: 385318
|
|
dashedName: semiprime
|
|
---
|
|
|
|
# --description--
|
|
|
|
Semiprime numbers are natural numbers that are products of exactly two (possibly equal) [prime numbers](https://rosettacode.org/wiki/prime_number).
|
|
|
|
<pre>1679 = 23 x 73</pre>
|
|
|
|
# --instructions--
|
|
|
|
Write a function that returns true if a number is semiprime, or false if it is not.
|
|
|
|
# --hints--
|
|
|
|
`isSemiPrime` should be a function.
|
|
|
|
```js
|
|
assert(typeof isSemiPrime === 'function');
|
|
```
|
|
|
|
`isSemiPrime(100)` should return a boolean.
|
|
|
|
```js
|
|
assert(typeof isSemiPrime(100) === 'boolean');
|
|
```
|
|
|
|
`isSemiPrime(100)` should return `false`.
|
|
|
|
```js
|
|
assert.equal(isSemiPrime(100), false);
|
|
```
|
|
|
|
`isSemiPrime(504)` should return `false`.
|
|
|
|
```js
|
|
assert.equal(isSemiPrime(504), false);
|
|
```
|
|
|
|
`isSemiPrime(4)` should return `true`.
|
|
|
|
```js
|
|
assert.equal(isSemiPrime(4), true);
|
|
```
|
|
|
|
`isSemiPrime(46)` should return `true`.
|
|
|
|
```js
|
|
assert.equal(isSemiPrime(46), true);
|
|
```
|
|
|
|
`isSemiPrime(13)` should return `false`.
|
|
|
|
```js
|
|
assert.equal(isSemiPrime(13), false);
|
|
```
|
|
|
|
`isSemiPrime(74)` should return `true`.
|
|
|
|
```js
|
|
assert.equal(isSemiPrime(74), true);
|
|
```
|
|
|
|
`isSemiPrime(1679)` should return `true`.
|
|
|
|
```js
|
|
assert.equal(isSemiPrime(1679), true);
|
|
```
|
|
|
|
`isSemiPrime(2)` should return `false`.
|
|
|
|
```js
|
|
assert.equal(isSemiPrime(2), false);
|
|
```
|
|
|
|
`isSemiPrime(95)` should return `true`.
|
|
|
|
```js
|
|
assert.equal(isSemiPrime(95), true);
|
|
```
|
|
|
|
`isSemiPrime(124)` should return `false`.
|
|
|
|
```js
|
|
assert.equal(isSemiPrime(124), false);
|
|
```
|
|
|
|
# --seed--
|
|
|
|
## --seed-contents--
|
|
|
|
```js
|
|
function isSemiPrime(n) {
|
|
|
|
}
|
|
```
|
|
|
|
# --solutions--
|
|
|
|
```js
|
|
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;
|
|
}
|
|
```
|