|
1 | | -function isPrime (n) { |
2 | | - let prime = false |
3 | | - |
4 | | - if (n > 1) { |
5 | | - for (let i = 2; i < n; i++) { |
6 | | - if (n % i === 0) { |
7 | | - prime = true |
8 | | - break |
9 | | - } |
10 | | - } |
11 | | - } |
12 | | - |
13 | | - return !prime |
14 | | -} |
| 1 | +import { PrimeCheck } from './PrimeCheck' |
15 | 2 |
|
16 | 3 | /** |
17 | 4 | * @function twinPrime |
18 | 5 | * Gets the 'twin prime' of a prime number. |
19 | | - * @returns {Array} Either an array with the original [0], and the twin [1], or an empty array if one of the numbers are not prime. |
| 6 | + * |
| 7 | + * @param {Integer} n The number to find the twin prime of. |
| 8 | + * @returns {Integer} Either the twin, or -1 if n or n + 2 is not prime. |
| 9 | + * |
20 | 10 | * @see https://en.wikipedia.org/wiki/Twin_prime |
21 | | - * @example twinPrime(5) = [5, 7] |
22 | | - * @example twinPrime(4) = [] |
| 11 | + * |
| 12 | + * @example twinPrime(5) = 7 |
| 13 | + * @example twinPrime(4) = -1 |
23 | 14 | */ |
24 | 15 | function twinPrime (n) { |
25 | | - const result = [] |
26 | 16 | const prime = isPrime(n) |
27 | 17 |
|
28 | 18 | if (!prime) { |
29 | | - return [] |
| 19 | + return -1 |
30 | 20 | } |
31 | 21 |
|
32 | | - result.push(n) |
33 | | - |
34 | 22 | if (!isPrime(n + 2)) { |
35 | | - return [] |
| 23 | + return -1 |
36 | 24 | } |
37 | 25 |
|
38 | | - result.push(n + 2) |
39 | | - |
40 | | - return result |
| 26 | + return n + 2 |
41 | 27 | } |
42 | 28 |
|
43 | | -export { isPrime,twinPrime } |
| 29 | +export { twinPrime } |
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