求 N 的阶乘

public class Test7 {
public static void main(String[] args) {
int n = 5;
int ret = factor(n);
System.out.println("ret = " + ret);
}

public static int factor(int n) {
    if (n == 1) {
    return 1;
    }
    return n * factor(n - 1); // factor 调用函数自身
}

}