Question

怎样用java编写一个程序，从键盘上输入数n，计算并输出1！+2！...+n!的结果

另外再附上怎样编写阶乘的方法吧，谢谢

Answer 1

import java.util.ArrayList;import java.util.List;
import java.util.Scanner;

public class Test { public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
System.out.println("please enter a num : ");
int num = scan.nextInt();
System.out.println("factorial : " + compute(num,"*"));
System.out.println("sum : " + compute(num,"+"));
}
public static int m3(int num,String sign){
if(num == 1){
return num;
}
return sign.charAt(0) == '+' ? num + m3(num - 1,sign) : sign.charAt(0) == '*' ? num * m3(num - 1,sign) : 0;
}
public static long compute(int num,String sign){
long res = 1;
if (sign.charAt(0) == '+') {
for (int i = 1; i <= num; i++) {
res += m3(i,sign);
}
res --;
}else if(sign.charAt(0) == '*'){
for (int i = 1; i <= num; i++) {
res *= m3(i,sign);
}
}else{
return -1;
}
return res;
}
}