階層求和

用不一樣方法實現求1!+2!+3!+…+20!
 循環算法求1!+2!+3!+...+20!
 遞歸算法求1!+2!+3!+...+20!

public class Text {
    public static void main(String args[]) {
        Text t = new Text();
        System.out.print(t.sum());
    }
    public int sum() {
        int a = 0;
        for (int i = 1; i <= 10; i++) {
            int b = 1;
            for (int j = 1; j <= i; j++) {
                bb = b * j;
            }
            aa = a + b;
        }
        return a;
    }
}

 

public class Text {
    public static long fac(int n) {
        long res = 1;
        for (int k = 1; k <= n; k++)
            res *= k;
        return res;
    }
    public static void main(String args[]) throws IOException {
        long sum = 0;
        int i = 1, n = 20;
        for (i = 1; i <= n; i++)
            sum += fac(i);
        System.out.println("前" + n + "項階乘的爲：" + sum);
    }
}

下面這個是遞歸嗎？？ 和上面貌似如出一轍的啊！！！