Change project structure to a Maven Java project + Refactor (#2816)

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

@@ -0,0 +1,40 @@
+package com.thealgorithms.maths;
+
+/**
+ * @author https://github.com/shellhub/
+ */
+public class GCDRecursion {
+
+    public static void main(String[] args) {
+        System.out.println(gcd(20, 15));
+        /* output: 5 */
+        System.out.println(gcd(10, 8));
+        /* output: 2 */
+        System.out.println(gcd(gcd(10, 5), gcd(5, 10)));
+        /* output: 5 */
+    }
+
+    /**
+     * get greatest common divisor
+     *
+     * @param a the first number
+     * @param b the second number
+     * @return gcd
+     */
+    public static int gcd(int a, int b) {
+
+        if (a < 0 || b < 0) {
+            throw new ArithmeticException();
+        }
+
+        if (a == 0 || b == 0) {
+            return Math.abs(a - b);
+        }
+
+        if (a % b == 0) {
+            return b;
+        } else {
+            return gcd(b, a % b);
+        }
+    }
+}