fix & optimize gcd function

- handle gcd of negative numbers
- fix the case when one of the numbers is equal to zero, gcd(0, x) = absolute value of x
- optimize using modulo instead of repeated subtractions

Author: os-moussao

src/ts/algorithms/math/gcd.ts

@@ -1,14 +1,17 @@
 export const gcd = (num1: number, num2: number): number => {
-  if (num1 === 0 || num2 === 0) {
-    return 0;
+  if (num1 < 0 || num2 < 0) {
+    return gcd(Math.abs(num1), Math.abs(num2));
   }
-  if (num1 === num2) {
+  if (num1 === 0) {
+    return num2;
+  }
+  if (num2 === 0) {
     return num1;
   }
   if (num1 > num2) {
-    return gcd(num1 - num2, num2);
+    return gcd(num1 % num2, num2);
   }
-  return gcd(num1, num2 - num1);
+  return gcd(num1, num2 % num1);
 };
 
 export const gcdArray = (num: number[]) => {