Refactor GCD: rename to Gcd, add docs, clean up

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: williamfiset

README.md

@@ -245,7 +245,7 @@ $ java -cp classes com.williamfiset.algorithms.search.BinarySearch
 - [Totient function (phi function, relatively prime number count)](src/main/java/com/williamfiset/algorithms/math/EulerTotientFunction.java) **- O(n<sup>1/4</sup>)**
 - [Totient function using sieve (phi function, relatively prime number count)](src/main/java/com/williamfiset/algorithms/math/EulerTotientFunctionWithSieve.java) **- O(nlog(log(n)))**
 - [Extended euclidean algorithm](src/main/java/com/williamfiset/algorithms/math/ExtendedEuclideanAlgorithm.java) **- ~O(log(a + b))**
-- [Greatest Common Divisor (GCD)](src/main/java/com/williamfiset/algorithms/math/GCD.java) **- ~O(log(a + b))**
+- [Greatest Common Divisor (GCD)](src/main/java/com/williamfiset/algorithms/math/Gcd.java) **- ~O(log(a + b))**
 - [Fast Fourier transform (quick polynomial multiplication)](src/main/java/com/williamfiset/algorithms/math/FastFourierTransform.java) **- O(nlog(n))**
 - [Fast Fourier transform (quick polynomial multiplication, complex numbers)](src/main/java/com/williamfiset/algorithms/math/FastFourierTransformComplexNumbers.java) **- O(nlog(n))**
 - [Primality check](src/main/java/com/williamfiset/algorithms/math/IsPrime.java) **- O(√n)**

src/main/java/com/williamfiset/algorithms/math/BUILD

@@ -35,10 +35,10 @@ java_binary(
     runtime_deps = [":math"],
 )
 
-# bazel run //src/main/java/com/williamfiset/algorithms/math:GCD
+# bazel run //src/main/java/com/williamfiset/algorithms/math:Gcd
 java_binary(
-    name = "GCD",
-    main_class = "com.williamfiset.algorithms.math.GCD",
+    name = "Gcd",
+    main_class = "com.williamfiset.algorithms.math.Gcd",
     runtime_deps = [":math"],
 )
 

src/main/java/com/williamfiset/algorithms/math/GCD.java

@@ -0,0 +1,34 @@
+/**
+ * Computes the Greatest Common Divisor (GCD) of two numbers using the Euclidean algorithm.
+ *
+ * <p>Time: ~O(log(a + b))
+ *
+ * @author William Fiset, william.alexandre.fiset@gmail.com
+ */
+package com.williamfiset.algorithms.math;
+
+public class Gcd {
+
+  /**
+   * Computes the Greatest Common Divisor (GCD) of a and b. The returned value is always
+   * non-negative.
+   */
+  public static long gcd(long a, long b) {
+    if (b == 0)
+      return Math.abs(a);
+    return gcd(b, a % b);
+  }
+
+  public static void main(String[] args) {
+    System.out.println(gcd(12, 18));   // 6
+    System.out.println(gcd(-12, 18));  // 6
+    System.out.println(gcd(12, -18));  // 6
+    System.out.println(gcd(-12, -18)); // 6
+
+    System.out.println(gcd(5, 0));  // 5
+    System.out.println(gcd(0, 5));  // 5
+    System.out.println(gcd(-5, 0)); // 5
+    System.out.println(gcd(0, -5)); // 5
+    System.out.println(gcd(0, 0));  // 0
+  }
+}