add new game

Author: Aleksandr Pronichev

app/src/main/java/hexlet/code/games/GCD.java

@@ -0,0 +1,31 @@
+package hexlet.code.games;
+
+import hexlet.code.Engine;
+
+public class GCD {
+
+    private static final String RULES = "Find the greatest common divisor of given numbers.";
+
+    public static void gameGCD() {
+        String[] questions = new String[Engine.ROUNDS];
+        String[] correctAnswers = new String[Engine.ROUNDS];
+
+        for (int i = 0; i < Engine.ROUNDS; i++) {
+            int firstNumber = (int) (Math.random() * 100);
+            int secondNumber = (int) (Math.random() * 100);
+            questions[i] = firstNumber + " " + secondNumber;
+            int gcd = calculateGCD(firstNumber, secondNumber);
+            correctAnswers[i] = Integer.toString(gcd);
+        }
+        Engine.game(RULES, questions, correctAnswers);
+    }
+
+    public static int calculateGCD(int a, int b) {
+        while (b != 0) {
+            int tmp = b;
+            b = a % b;
+            a = tmp;
+        }
+        return a;
+    }
+}