2、阶乘

基础版 求5的阶乘

//循环写法
    public static int getMut(int num){
        int mut = 1;
        for(int i = num;i > 0;i--){
            mut *= i;
        }
        return mut;
    }
    public static void main(String[] args) {
        int mut = getMut(5);
        System.out.println(mut);
    }

//递归写法
    public static int getMut1(int num){
        if(num == 1){
            return 1;
        }else{
            return num * getMut1(num - 1);
        }
    }
    public static void main(String[] args) {
        int mut1 = getMut1(5);
        System.out.println(mut1);
    }

升级版 求5!+4!+3!+2!+1!

    public static int getMut2(int num){
        if(num == 1){
            return 1;
        }else{
            return num * getMut1(num - 1);
        }
    }
    public static void main(String[] args) {
        int sum = 0;
        for(int i = 5;i > 0;i--){
            int mut2 = getMut2(i);
            sum += mut2;
        }
        System.out.println(sum);
    }