add method

CHANGELOG.md

@@ -3,7 +3,7 @@
 
 -------------------------------------------------------------------------------------------------------------
 
-# 5.6.0 (2021-03-05)
+# 5.6.0 (2021-03-07)
 
 ### 新特性
 * 【poi    】     重要：不再兼容POI-3.x，增加兼容POI-5.x（issue#I35J6B@Gitee）
@@ -12,6 +12,7 @@
 * 【crypto 】     增加PBKDF2（issue#1416@Github）
 * 【core   】     增加FuncKeyMap（issue#1402@Github）
 * 【core   】     增加StrMatcher（issue#1379@Github）
+* 【core   】     NumberUtil增加factorial针对BigInterger方法（issue#1379@Github）
 
 ### Bug修复
 * 【socket 】     修复Client创建失败资源未释放问题。

hutool-core/src/main/java/cn/hutool/core/util/NumberUtil.java

@@ -1428,10 +1428,62 @@ public class NumberUtil {
 
 	// ------------------------------------------------------------------------------------------- others
 
+	/**
+	 * 计算阶乘
+	 * <p>
+	 * n! = n * (n-1) * ... * 2 * 1
+	 * </p>
+	 *
+	 * @param n 阶乘起始
+	 * @return 结果
+	 * @since 5.6.0
+	 */
+	public static BigInteger factorial(BigInteger n) {
+		if(n.equals(BigInteger.ZERO)){
+			return BigInteger.ONE;
+		}
+		return factorial(n, BigInteger.ZERO);
+	}
+
 	/**
 	 * 计算范围阶乘
 	 * <p>
-	 * factorial(start, end) = start * (start - 1) * ... * (end - 1)
+	 * factorial(start, end) = start * (start - 1) * ... * (end + 1)
+	 * </p>
+	 *
+	 * @param start 阶乘起始（包含）
+	 * @param end   阶乘结束，必须小于起始（不包括）
+	 * @return 结果
+	 * @since 5.6.0
+	 */
+	public static BigInteger factorial(BigInteger start, BigInteger end) {
+		Assert.notNull(start, "Factorial start must be not null!");
+		Assert.notNull(end, "Factorial end must be not null!");
+		if(start.compareTo(BigInteger.ZERO) < 0 || end.compareTo(BigInteger.ZERO) < 0){
+			throw new IllegalArgumentException(StrUtil.format("Factorial start and end both must be > 0, but got start={}, end={}", start, end));
+		}
+
+		if (start.equals(BigInteger.ZERO)){
+			start = BigInteger.ONE;
+		}
+
+		if(end.compareTo(BigInteger.ONE) < 0){
+			end = BigInteger.ONE;
+		}
+
+		BigInteger result = start;
+		end = end.add(BigInteger.ONE);
+		while(start.compareTo(end) > 0) {
+			start = start.subtract(BigInteger.ONE);
+			result = result.multiply(start);
+		}
+		return result;
+	}
+
+	/**
+	 * 计算范围阶乘
+	 * <p>
+	 * factorial(start, end) = start * (start - 1) * ... * (end + 1)
 	 * </p>
 	 *
 	 * @param start 阶乘起始（包含）

hutool-core/src/test/java/cn/hutool/core/util/NumberUtilTest.java

@@ -5,6 +5,7 @@ import org.junit.Assert;
 import org.junit.Test;
 
 import java.math.BigDecimal;
+import java.math.BigInteger;
 import java.math.RoundingMode;
 import java.util.Set;
 
@@ -308,6 +309,24 @@ public class NumberUtilTest {
 		Assert.assertEquals(2432902008176640000L, NumberUtil.factorial(20, 0));
 	}
 
+	@Test
+	public void factorialTest2(){
+		long factorial = NumberUtil.factorial(new BigInteger("0")).longValue();
+		Assert.assertEquals(1, factorial);
+
+		Assert.assertEquals(1L, NumberUtil.factorial(new BigInteger("1")).longValue());
+		Assert.assertEquals(1307674368000L, NumberUtil.factorial(new BigInteger("15")).longValue());
+		Assert.assertEquals(2432902008176640000L, NumberUtil.factorial(20));
+
+		factorial = NumberUtil.factorial(new BigInteger("5"), new BigInteger("0")).longValue();
+		Assert.assertEquals(120, factorial);
+		factorial = NumberUtil.factorial(new BigInteger("5"), BigInteger.ONE).longValue();
+		Assert.assertEquals(120, factorial);
+
+		Assert.assertEquals(5, NumberUtil.factorial(new BigInteger("5"), new BigInteger("4")).longValue());
+		Assert.assertEquals(2432902008176640000L, NumberUtil.factorial(new BigInteger("20"), BigInteger.ZERO).longValue());
+	}
+
 	@Test
 	public void mulTest(){
 		final BigDecimal mul = NumberUtil.mul(new BigDecimal("10"), null);