feat: add gcd

src/main/java/me/hatter/math/util/MathUtil.java

@@ -46,6 +46,16 @@ public class MathUtil {
         return v.add(BigDecimal.valueOf(nums[0]));
     }
 
+    // https://oi-wiki.org/math/number-theory/gcd/
+    public static BigInteger gcd(BigInteger a, BigInteger b) {
+        while (b.compareTo(BigInteger.ZERO) != 0) {
+            BigInteger tmp = a;
+            a = b;
+            b = tmp.mod(b);
+        }
+        return a;
+    }
+
     // Newton-Raphson法によるBigDecimalの平方根計算
     public static BigDecimal sqrt(BigDecimal n, int scale) {
         if (n.compareTo(BigDecimal.ZERO) < 0) {

src/test/java/me/hatter/math/util/MathUtilTest.java

@@ -4,6 +4,7 @@ import org.junit.Assert;
 import org.junit.Test;
 
 import java.math.BigDecimal;
+import java.math.BigInteger;
 import java.math.RoundingMode;
 
 public class MathUtilTest {
@@ -66,4 +67,12 @@ public class MathUtilTest {
                 MathUtil.sqrt(BigDecimal.valueOf(10), 100)
         );
     }
+
+    @Test
+    public void testGcd() {
+        Assert.assertEquals(BigInteger.valueOf(1), MathUtil.gcd(BigInteger.valueOf(1), BigInteger.valueOf(3)));
+        Assert.assertEquals(BigInteger.valueOf(1), MathUtil.gcd(BigInteger.valueOf(3), BigInteger.valueOf(7)));
+        Assert.assertEquals(BigInteger.valueOf(4), MathUtil.gcd(BigInteger.valueOf(12), BigInteger.valueOf(8)));
+        Assert.assertEquals(BigInteger.valueOf(1), MathUtil.gcd(BigInteger.valueOf(7), BigInteger.valueOf(11)));
+    }
 }