JavaSE中你想看的例子——递归（1-20阶乘之和）

求1! + 2! + 3! + ... + 20! 的和

 

方法一（递归）：找规律，找出口

public class Test01 {public static void main(String[] args) {long sum = 0;for (int i = 1; i <= 20; i++) {sum = sum + DiGui(i);}System.out.println(sum);}public static long DiGui(int a) {if (a == 1) {return 1;     //递归的出口}else{return a*DiGui(a-1);}}
}

 

 

方法二（for循环）：

public class Test01 {public static void main(String[] args) {long sum = 0;for (int i = 1; i <= 20; i++) {long c = 1;for (int j = 1; j <= i; j++) {c = c * j;}s = s + c;}System.out.println(s);}
}