feat: add bin pow

README.md

@@ -11,6 +11,7 @@
 | EulerNumber             | 欧拉数                | [eulers-number](https://hatter.ink/static/resource/muboard/?id=eulers-number&version=latest&full=1)                         |
 | BirthdayParadox         | 生日悖论               | [birthday-paradox](https://hatter.ink/static/resource/muboard/?id=birthday-paradox&version=latest&full=1)                   |
 | ChudnovskyAlgorithm     | 楚德诺夫斯基算法           | [chudnovsky-algorithm](https://hatter.ink/static/resource/muboard/?id=chudnovsky-algorithm&version=latest&full=1)           |
+| BinaryExponentiation    | 快速幂                | [binary-exponentiation](https://hatter.ink/static/resource/muboard/?id=binary-exponentiation&version=1)                     |
 
 
 <br>

src/main/java/me/hatter/math/BinaryExponentiation.java

@@ -0,0 +1,35 @@
+package me.hatter.math;
+
+import java.math.BigInteger;
+import java.util.Arrays;
+
+// https://oi-wiki.org/math/binary-exponentiation/
+public class BinaryExponentiation {
+
+    public static void main(String[] args) {
+        System.out.println(binPow(BigInteger.valueOf(2), BigInteger.valueOf(100)));
+
+        for (int i = 0; i < 100; i++) {
+            for (int j = 0; j < 100; j++) {
+                BigInteger a = BigInteger.valueOf(i).pow(j);
+                BigInteger b = binPow(BigInteger.valueOf(i), BigInteger.valueOf(j));
+
+                if (a.compareTo(b) != 0) {
+                    System.out.println(Arrays.asList(i, j, a, b));
+                }
+            }
+        }
+    }
+
+    public static BigInteger binPow(BigInteger a, BigInteger b) {
+        BigInteger result = BigInteger.ONE;
+        while (b.compareTo(BigInteger.ZERO) > 0) {
+            if (b.mod(BigInteger.valueOf(2)).compareTo(BigInteger.ONE) == 0) {
+                result = result.multiply(a);
+            }
+            a = a.multiply(a);
+            b = b.divide(BigInteger.valueOf(2));
+        }
+        return result;
+    }
+}

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

@@ -46,6 +46,14 @@ public class MathUtil {
         return v.add(BigDecimal.valueOf(nums[0]));
     }
 
+    public static BigInteger max(BigInteger a, BigInteger b) {
+        return (a.compareTo(b) < 0) ? b : a;
+    }
+
+    public static BigInteger min(BigInteger a, BigInteger b) {
+        return (a.compareTo(b) < 0) ? a : b;
+    }
+
     // https://oi-wiki.org/math/number-theory/gcd/
     public static BigInteger gcd(BigInteger a, BigInteger b) {
         while (b.compareTo(BigInteger.ZERO) != 0) {

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

@@ -48,6 +48,16 @@ public class MathUtilTest {
         ));
     }
 
+    @Test
+    public void testMinMax() {
+        Assert.assertEquals(BigInteger.valueOf(10), MathUtil.max(BigInteger.valueOf(1), BigInteger.valueOf(10)));
+        Assert.assertEquals(BigInteger.valueOf(10), MathUtil.max(BigInteger.valueOf(10), BigInteger.valueOf(9)));
+        Assert.assertEquals(BigInteger.valueOf(10), MathUtil.max(BigInteger.valueOf(10), BigInteger.valueOf(10)));
+        Assert.assertEquals(BigInteger.valueOf(10), MathUtil.min(BigInteger.valueOf(10), BigInteger.valueOf(10)));
+        Assert.assertEquals(BigInteger.valueOf(1), MathUtil.min(BigInteger.valueOf(1), BigInteger.valueOf(10)));
+        Assert.assertEquals(BigInteger.valueOf(9), MathUtil.min(BigInteger.valueOf(10), BigInteger.valueOf(9)));
+    }
+
     @Test
     public void testSqrt() {
         Assert.assertEquals(