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147 lines
2.6 KiB
Markdown
147 lines
2.6 KiB
Markdown
---
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id: 5eb3e4aa847216613aa81983
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title: Halbprimzahl
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challengeType: 1
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forumTopicId: 385318
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dashedName: semiprime
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---
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# --description--
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Semiprime numbers are natural numbers that are products of exactly two (possibly equal) <a href="https://rosettacode.org/wiki/prime_number" target="_blank" rel="noopener noreferrer nofollow">prime numbers</a>.
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<pre>1679 = 23 x 73</pre>
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# --instructions--
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Schreibe eine Funktion, die true zurückgibt, wenn eine Zahl halbzahlig ist, oder false, wenn sie es nicht ist.
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# --hints--
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`isSemiPrime` sollte eine Funktion sein.
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```js
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assert(typeof isSemiPrime === 'function');
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```
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`isSemiPrime(100)` sollte einen Boolean zurückgeben.
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```js
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assert(typeof isSemiPrime(100) === 'boolean');
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```
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`isSemiPrime(100)` sollte `false` zurückgeben.
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```js
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assert.equal(isSemiPrime(100), false);
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```
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`isSemiPrime(504)` sollte `false` zurückgeben.
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```js
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assert.equal(isSemiPrime(504), false);
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```
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`isSemiPrime(4)` sollte `true` zurückgeben.
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```js
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assert.equal(isSemiPrime(4), true);
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```
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`isSemiPrime(46)` sollte `true` zurückgeben.
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```js
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assert.equal(isSemiPrime(46), true);
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```
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`isSemiPrime(13)` sollte `false` zurückgeben.
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```js
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assert.equal(isSemiPrime(13), false);
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```
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`isSemiPrime(74)` sollte `true` zurückgeben.
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```js
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assert.equal(isSemiPrime(74), true);
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```
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`isSemiPrime(1679)` sollte `true` zurückgeben.
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```js
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assert.equal(isSemiPrime(1679), true);
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```
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`isSemiPrime(2)` sollte `false` zurückgeben.
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```js
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assert.equal(isSemiPrime(2), false);
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```
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`isSemiPrime(95)` sollte `true` zurückgeben.
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```js
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assert.equal(isSemiPrime(95), true);
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```
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`isSemiPrime(124)` sollte `false` zurückgeben.
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```js
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assert.equal(isSemiPrime(124), false);
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```
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# --seed--
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## --seed-contents--
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```js
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function isSemiPrime(n) {
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}
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```
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# --solutions--
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```js
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function isSemiPrime(n) {
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if (n <= 3) return false;
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var ans = [];
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var done = false;
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while (!done) {
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if (n % 2 === 0) {
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ans.push(2);
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n /= 2;
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continue;
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}
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if (n % 3 === 0) {
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ans.push(3);
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n /= 3;
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continue;
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}
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if (n === 1) return ans.length == 2;
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var sr = Math.sqrt(n);
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done = true;
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// try to divide the checked number by all numbers till its square root.
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for (var i = 6; i <= sr; i += 6) {
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if (n % (i - 1) === 0) {
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// is n divisible by i-1?
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ans.push(i - 1);
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n /= i - 1;
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done = false;
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break;
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}
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if (n % (i + 1) === 0) {
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// is n divisible by i+1?
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ans.push(i + 1);
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n /= i + 1;
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done = false;
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break;
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}
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}
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}
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ans.push(n);
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return ans.length == 2;
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}
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```
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