add gcd

realDuYuanChao · realDuYuanChao · commit 4832c6f25960 · 2020-10-22T10:27:13.000+08:00
diff --git a/src/main/java/com/examplehub/maths/GreatestCommonDivisor.java b/src/main/java/com/examplehub/maths/GreatestCommonDivisor.java
@@ -0,0 +1,37 @@
+package com.examplehub.maths;
+
+/**
+ * https://en.wikipedia.org/wiki/Greatest_common_divisor
+ */
+public class GreatestCommonDivisor {
+
+    /**
+     * Returns the greatest common divisor of two numbers.
+     *
+     * @param a the first number the.
+     * @param b the second number.
+     * @return the greatest common divisor of two numbers.
+     */
+    public static int gcdEasy(int a, int b) {
+        if (a == 0 || b == 0) {
+            return Math.max(a, b);
+        }
+        for (int i = Math.min(a, b); i >= 1; i--) {
+            if (a % i == 0 && b % i == 0) {
+                return i;
+            }
+        }
+        return -1; /* not found */
+    }
+
+    /**
+     * Returns the greatest common divisor of two numbers.
+     *
+     * @param a the first number the.
+     * @param b the second number.
+     * @return the greatest common divisor of two numbers.
+     */
+    public static int gcd(int a, int b) {
+        return b == 0 ? a : gcd(b, a % b);
+    }
+}
diff --git a/src/test/java/com/examplehub/maths/GreatestCommonDivisorTest.java b/src/test/java/com/examplehub/maths/GreatestCommonDivisorTest.java
@@ -0,0 +1,16 @@
+package com.examplehub.maths;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class GreatestCommonDivisorTest {
+    @Test
+    void testGCD() {
+        int[][] testNumbers = {{8, 12, 4}, {54, 24, 6}, {3, 4, 1}, {3, 0, 3}};
+        for (int[] testNumber : testNumbers) {
+            assertEquals(testNumber[2], GreatestCommonDivisor.gcdEasy(testNumber[0], testNumber[1]));
+            assertEquals(testNumber[2], GreatestCommonDivisor.gcd(testNumber[0], testNumber[1]));
+        }
+    }
+}
