Java中求阶乘的算法 博客分类： Java 算法Java

Java中求阶乘的算法

1.一般算法：

public class Factorial {
	public static int factorial(int n) {
		if (n < 0 || n > 16) {
			System.err.println("n must be great than 0 and less than 17");
			return -1;
		} else if (n == 0) {
			return 1;
		} else {
			int result = 1;
			for (int i = 1; i <= n; i++) {
				result *= i;
			}
			return result;
		}
	}

	public static void main(String args[]) {
		System.out.println("result = " + factorial(5));
	}
} 

   运行结果：result = 120

 

2.递归算法：

public class Factorial {
	public static int recursion(int n) {
		if (n < 0 || n > 16) {
			System.err.println("n must be great than 0 and less than 17");
			return -1;
		} else if (n == 0) {
			return 1;
		} else {
			return n * recursion(n - 1);
		}
	}

	public static void main(String[] args) {
		System.out.println("result = " + recursion(16));
	}
}

 运行结果：result = 2004189184

 

3.使用BigInteger

import java.math.BigInteger;

public class Factorial {
	public static BigInteger bigInteger(int n) {
		BigInteger result = new BigInteger("1");
		if (n < 0) {
			System.err.println("n must be great than 0");
			return new BigInteger("-1");
		} else if (n == 0) {
			return new BigInteger("1");
		} else {
			for (int i = 1; i <= n; i++) {
				BigInteger num = new BigInteger(String.valueOf(i));
				result = result.multiply(num);
			}
			return result;
		}
	}

	public static void main(String[] args) {
		System.out.println("result = " + bigInteger(100));
	}
}

 运行结果：result = 93326215443944152681699238856266700490715968264381621468592963895

217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000