49.求指定项数阶乘的和

编程题目：

49.求1+2!+3!+…+20!的和。

示例代码：

package program.calculation.exercise49;

import java.util.Scanner;

/**
* 49.求1+2!+3!+...+20!的和。
*/

public class FactorialSum {
	public static void main(String[] args) {
		
		System.out.println("请输入项数：");
		@SuppressWarnings("resource")
		Scanner scanner = new Scanner(System.in);
		int n = scanner.nextInt();
		
		System.out.println("第一种方式（循环）：");
		System.out.println(n+"项阶乘之和为："+loopFactorialSum(n));
		
		System.out.println("第二种方式（递归）：");
		System.out.println(n+"项阶乘之和为："+recurFactorialSum(n));
		
	}

	//第一种方式：循环
	private static int loopFactorialSum(int n) {
		
		int sum = 0;
		for (int i=1; i<=n; i++) {
			int factorial = 1; //每项阶乘
			for (int j=1; j<=i; j++) {
				factorial *= j;
			}
			sum += factorial;
		}
		return sum;
		
	}
	
	//第二种方式：递归
	private static int recurFactorialSum(int n){
		
		int sum = 0;
		for(int i=1; i<=n; i++) {
			sum += recurFactorial(i);
		}
		return sum;
		
	}
	
	//求每项阶乘(递归)
	private static int recurFactorial(int n){
		
		if(1 == n || 2 == n){
			return n;
		}else{
			return n*recurFactorial(n-1);
		}
	}
	
}

结果显示：