Fix empty input handling in GCD (#4199)

src/main/java/com/thealgorithms/maths/GCD.java

@@ -33,15 +33,15 @@ public class GCD {
     }
 
     /**
-     * get greatest common divisor in array
+     * @brief computes gcd of an array of numbers
      *
-     * @param number contains number
-     * @return gcd
+     * @param numbers the input array
+     * @return gcd of all of the numbers in the input array
      */
-    public static int gcd(int[] number) {
-        int result = number[0];
-        for (int i = 1; i < number.length; i++) { // call gcd function (input two value)
-            result = gcd(result, number[i]);
+    public static int gcd(int[] numbers) {
+        int result = 0;
+        for (final var number : numbers) {
+            result = gcd(result, number);
         }
 
         return result;

src/test/java/com/thealgorithms/maths/GCDTest.java

@@ -48,4 +48,19 @@ public class GCDTest {
     void test7() {
         Assertions.assertEquals(GCD.gcd(9, 6), 3);
     }
+    
+    @Test
+    void testArrayGcd1() {
+        Assertions.assertEquals(GCD.gcd(new int[]{9, 6}), 3);
+    }
+
+    @Test
+    void testArrayGcd2() {
+        Assertions.assertEquals(GCD.gcd(new int[]{2*3*5*7, 2*5*5*5, 2*5*11, 5*5*5*13}), 5);
+    }
+    
+    @Test
+    void testArrayGcdForEmptyInput() {
+        Assertions.assertEquals(GCD.gcd(new int[]{}), 0);
+    }    
 }