P1009 [noip1998 popularization group] sum of factorials

Title Description
Calculate with high precision S = 1! + 2! + 3! +⋯+ n!S=1!+2!+3!+⋯+n!（n \le 50n≤50）.

among “!” It means factorial , for example ：5!=5×4×3×2×1.

Input format
A positive integer nn.

Output format
A positive integer SS, It means the result of calculation .

I/o sample
Input #1 Copy
3
Output #1 Copy
9
explain / Tips
【 Data range 】

about 100% The data of ,1≤n≤50.
Be careful ： General data types can only be saved n<=20 The data and , So here we use java Of BigInteger Class to calculate , Need to use BigInteger Class multiply Methods and add Method ！！！

import java.util.*;
import java.math.*;
public class Main{
    
    public static void main(String[]args){
    
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        BigInteger bi[] = new BigInteger[n+1];// Why? n+1, For better understanding and initialization . Define a n+1 BigInteger Array of classes 
        BigInteger biSum = new BigInteger("0");// Class instances for summation 
        for(int i = 1;i <= n;i++){
    
            bi[i] = new BigInteger(String.valueOf(i));// Initialize class array .
        }
        for(int i = 1;i <= n;i++){
    
            BigInteger temp = new BigInteger("1");// Temporary variable , Used to receive 1~n Factorial of each digit of 
            for(int j = 1 ;j <=i;j++){
    
                temp = temp.multiply(bi[j]);
            }
            biSum = biSum.add(temp);// Used to sum and save 1~n Sum of factorials of various numbers 
        }
        System.out.println(biSum);
    }
}