Project Euler #20: Factorial digit sum

Factorial digit sum (without BigInteger) - 我的博客 - ITeye技术网站

Factorial digit sum

n! means n × (n − 1) × ... × 3 × 2 × 1
For example, 10! = 10 × 9 × ... × 3 × 2 × 1 = 3628800,
and the sum of the digits in the number 10! is 3 + 6 + 2 + 8 + 8 + 0 + 0 = 27.
Find the sum of the digits in the number 100!

From: https://projecteuler.net/problem=20

1. public static int sumFactorialDigits(int n) {  
2.     int sum = 0, carry = 0;  
3.     int[] digits = new int[1000];  
4.     digits[0] = 1;  
5.     digits[1] = 1;  
6.     for (int k = 2; k < n + 1; k++) {  
7.         for (int i = 1; i <= digits[0]; i++) {  
8.             digits[i] = digits[i] * k + carry;  
9.             carry = 0;  
10.             if (digits[i] > 9) {  
11.                 carry = digits[i] / 10;  
12.                 digits[i] %= 10;  
13.                 if (i == digits[0])  
14.                     digits[0]++;  
15.             }  
16.         }  
17.     }  
18.     for (int i = digits[0]; i >= 1; i--)  
19.         sum += digits[i];  
20.     return sum;  
21. }  

https://chennaitechblog.wordpress.com/2013/05/24/factorial-digit-sum/

 public static void main(String args[])
 {
  long start_time= System.currentTimeMillis(); 
  BigInteger data= new BigInteger("1");
  for(int index=1;index<=100;++index)
   data= data.multiply(new BigInteger(index+""));
  String str=data.toString();
  
  long sum=0;
  
  for(int index=0;index<=str.length()-1;++index)
  sum+=Integer.parseInt(str.substring(index,index+1));
  
  System.out.println("The sum of the digits in the number 100! :"+sum);
  System.out.println("Total time taken:"+ ((System.currentTimeMillis()-start_time)/1000)+"sec");
  
 }

http://cupc71.blogspot.com/2015/01/project-euler-factorial-digit-sum.html
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