Fix & optimize gcd function

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[]) => {

test/ts/algorithms/math/gcd.spec.ts

@@ -3,14 +3,26 @@ import { expect } from 'chai';
 import { gcd } from '../../../../src/ts/index';
 
 describe('GCD', () => {
+  it('returns the correct GCD for positive numbers', () => {
+    expect(gcd(8, 12)).to.equal(4);
+    expect(gcd(15, 25)).to.equal(5);
+    expect(gcd(21, 28)).to.equal(7);
+  });
+
+  it('returns the correct GCD for negative numbers', () => {
+    expect(gcd(-8, 12)).to.equal(4);
+    expect(gcd(15, -25)).to.equal(5);
+    expect(gcd(-21, -28)).to.equal(7);
+  });
 
-  it('returns the gcd between two numbers', () => {
+  it('returns the correct GCD when one of the numbers is 0', () => {
+    expect(gcd(0, -12)).to.equal(12);
+    expect(gcd(15, 0)).to.equal(15);
+  });
 
-    expect(gcd(1, 0)).to.equal(0);
-    expect(gcd(1, 1)).to.equal(1);
-    expect(gcd(2, 2)).to.equal(2);
-    expect(gcd(2, 4)).to.equal(2);
-    expect(gcd(2, 3)).to.equal(1);
-    expect(gcd(10, 1000)).to.equal(10);
+  it('returns 1 for co-prime numbers', () => {
+    expect(gcd(7, 22)).to.equal(1);
+    expect(gcd(11, 28)).to.equal(1);
+    expect(gcd(9, 16)).to.equal(1);
   });
 });