Project Euler > Problem 20 > Factorial digit sum (Java Solution)

Problem:

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!

Solution:

648

Code:
The solution may include methods that will be found here: Library.java .

public interface EulerSolution{

public String run();

}

/* 
 * Solution to Project Euler problem 20
 * By Nayuki Minase
 * 
 * http://nayuki.eigenstate.org/page/project-euler-solutions
 * https://github.com/nayuki/Project-Euler-solutions
 */


public final class p020 implements EulerSolution {
 
 public static void main(String[] args) {
  System.out.println(new p020().run());
 }
 
 
 public String run() {
  String temp = Library.factorial(100).toString();
  int sum = 0;
  for (int i = 0; i < temp.length(); i++)
   sum += temp.charAt(i) - '0';
  return Integer.toString(sum);
 }
 
}