From aa7b95e6a156c03e5a3c0f04f6314566d8553660 Mon Sep 17 00:00:00 2001
From: vatsalgosar <vatsalgosar@gmail.com>
Date: Mon, 5 Aug 2019 23:28:19 +0530
Subject: [PATCH] BAEL-3115 - GCD implementation methods using Brute force,
 Euclid's Algo and Stein's Algo

---
 .../algorithms/gcd/GCDImplementation.java     | 51 +++++++++++++++++++
 .../gcd/GCDImplementationUnitTest.java        | 32 ++++++++++++
 2 files changed, 83 insertions(+)
 create mode 100644 java-math/src/main/java/com/baeldung/algorithms/gcd/GCDImplementation.java
 create mode 100644 java-math/src/test/java/com/baeldung/algorithms/gcd/GCDImplementationUnitTest.java

diff --git a/java-math/src/main/java/com/baeldung/algorithms/gcd/GCDImplementation.java b/java-math/src/main/java/com/baeldung/algorithms/gcd/GCDImplementation.java
new file mode 100644
index 0000000000..df12c97162
--- /dev/null
+++ b/java-math/src/main/java/com/baeldung/algorithms/gcd/GCDImplementation.java
@@ -0,0 +1,51 @@
+package com.baeldung.algorithms.gcd;
+
+public class GCDImplementation {
+
+    public static int gcdByBruteForce(int n1, int n2) {
+        int gcd = 1;
+        for (int i = 1; i <= n1 && i <= n2; i++)
+            if (n1 % i == 0 && n2 % i == 0)
+                gcd = i;
+
+        return gcd;
+    }
+
+    public static int gcdByEuclidsAlgorithm(int n1, int n2) {
+        if (n2 == 0)
+            return n1;
+        return gcdByEuclidsAlgorithm(n2, n1 % n2);
+    }
+
+    public static int gcdBySteinsAlgorithm(int n1, int n2) {
+
+        if (n1 == 0)
+            return n2;
+
+        if (n2 == 0)
+            return n1;
+
+        int n;
+        for (n = 0; ((n1 | n2) & 1) == 0; n++) {
+            n1 >>= 1;
+            n2 >>= 1;
+        }
+
+        while ((n1 & 1) == 0)
+            n1 >>= 1;
+
+        do {
+            while ((n2 & 1) == 0)
+                n2 >>= 1;
+
+            if (n1 > n2) {
+                int temp = n1;
+                n1 = n2;
+                n2 = temp;
+            }
+            n2 = (n2 - n1);
+        } while (n2 != 0);
+
+        return n1 << n;
+    }
+}
diff --git a/java-math/src/test/java/com/baeldung/algorithms/gcd/GCDImplementationUnitTest.java b/java-math/src/test/java/com/baeldung/algorithms/gcd/GCDImplementationUnitTest.java
new file mode 100644
index 0000000000..d2c91a2eb8
--- /dev/null
+++ b/java-math/src/test/java/com/baeldung/algorithms/gcd/GCDImplementationUnitTest.java
@@ -0,0 +1,32 @@
+package com.baeldung.algorithms.gcd;
+
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class GCDImplementationUnitTest {
+
+    @Test
+    public void whenCalculatingGCDByBruteForceMethod_thenCorrect() {
+        int n1 = 60;
+        int n2 = 90;
+        int gcd = GCDImplementation.gcdByBruteForce(n1, n2);
+        assertThat(gcd).isEqualTo(30);
+    }
+
+    @Test
+    public void whenCalculatingGCDByEuclidsAlgorithm_thenCorrect() {
+        int n1 = 60;
+        int n2 = 90;
+        int gcd = GCDImplementation.gcdByEuclidsAlgorithm(n1, n2);
+        assertThat(gcd).isEqualTo(30);
+    }
+
+    @Test
+    public void whenCalculatingGCDBySteinsAlgorithm_thenCorrect() {
+        int n1 = 60;
+        int n2 = 90;
+        int gcd = GCDImplementation.gcdBySteinsAlgorithm(n1, n2);
+        assertThat(gcd).isEqualTo(30);
+    }
+}