Merge pull request #470 from kriadmin/patch-4

Create factors.md

snippets/factors.md

@@ -0,0 +1,35 @@
+### factors
+
+Returns the array of factors of the given `num`. 
+If the second argument is set to `true` returns only the prime factors of `num`.
+If `num` is `1` or `0` returns an empty array.
+If `num` is less than `0` returns all the factors of `-int` together with their additive inverses.
+
+Use `Array.from()`, `Array.map()` and `Array.filter()` to find all the factors of `num`.
+If given `num` is negative, use `Array.reduce()` to add the additive inverses to the array.
+Return all results if `primes` is `false`, else determine and return only the prime factors using `isPrime` and `Array.filter()`.
+Omit the second argument, `primes`, to return prime and non-prime factors by default.
+
+**Note**:- _Negative numbers are not considered prime._
+
+``` js
+const factors = (num, primes = false) => {
+  const isPrime = num => {
+    const boundary = Math.floor(Math.sqrt(num));
+    for (var i = 2; i <= boundary; i++) if (num % i === 0) return false;
+    return num >= 2;
+  }
+  const isNeg = num < 0;
+  num = isNeg ? -num : num;
+  let array = Array.from({length: num - 1}).map((val,i) => num % (i+2) === 0 ? (i+2) : false).filter(val => val);
+  if(isNeg) array = array.reduce((acc,val) => {acc.push(val); acc.push(-val); return acc}, []);
+  return primes ? array.filter(isPrime) : array;
+}
+```
+
+```js
+factors(12); // [2,3,4,6,12]
+factors(12,true); // [2,3]
+factors(-12); // [2, -2, 3, -3, 4, -4, 6, -6, 12, -12]
+factors(-12, true); // [2,3]
+```