大数阶乘问题

日后整理

import java.math.BigInteger;

public class Factorial {

    public static void main(String[] args) {
        // System.out.println(recursion(0));
        // System.out.println(circulation(1));
        System.out.println(bigInteger(100));
    }

    /**
     * 方法一 迭代实现阶乘
     */
    public static int recursion(int n) {
        int sum = 1;
        if (n < 0)
            throw new IllegalArgumentException("必须为正整数");
        if (n == 1 || n == 0) {
            return sum;
        } else {
            sum = n * recursion(n - 1);
            return sum;
        }
        // return sum;

    }

    /**
     * 方法二 循环实现阶乘
     */
    public static int circulation(int n) {
        int sum = 1;
        if (n >= 0) {
            if (n == 0 || n == 1) {
                return 1;
            } else {
                int i = 1;
                while (i <= n) {
                    sum = sum * n;
                    n--;
                }
                return sum;
            }
        } else
            throw new IllegalArgumentException("传入参数非法！");
        // return sum;
    }

    /**
     * 方法三 利用BigInteger类
     */

    public static BigInteger bigInteger(int n) {
        BigInteger sum = new BigInteger("1");
        if (n >= 0) {
            if (n == 0 || n == 1) {
                return BigInteger.valueOf(1);
            } else {
                int i = 1;
                while (i <= n) {
                    sum = sum.multiply(BigInteger.valueOf(n));
                    n--;
                }
                return sum;
            }
        } else
            throw new IllegalArgumentException("传入参数非法！");
    }

}

 http://ly5633.iteye.com/blog/1219408

http://www.it165.net/pro/html/201409/21349.html

http://blog.csdn.net/liyong199012/article/details/40341779