Project Euler > Problem 34 > Digit factorials (Java Solution)

Problem:

145 is a curious number, as 1! + 4! + 5! = 1 + 24 + 120 = 145.

Find the sum of all numbers which are equal to the sum of the factorial of their digits.

Note: as 1! = 1 and 2! = 2 are not sums they are not included.

Solution:

40730

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

public interface EulerSolution{

public String run();

}

/* 
 * Solution to Project Euler problem 34
 * By Nayuki Minase
 * 
 * http://nayuki.eigenstate.org/page/project-euler-solutions
 * https://github.com/nayuki/Project-Euler-solutions
 */


public final class p034 implements EulerSolution {
 
 public static void main(String[] args) {
  System.out.println(new p034().run());
 }
 
 
 public String run() {
  // As stated in the problem, 1 = 1! and 2 = 2! are excluded.
  // If a number has at least n >= 8 digits, then even if every digit is 9,
  // n * 9! is still less than the number (which is at least 10^n).
  int sum = 0;
  for (int i = 3; i < 10000000; i++) {
   if (i == factorialDigitSum(i))
    sum += i;
  }
  return Integer.toString(sum);
 }
 
 
 // Hard-coded values for factorial(0), factorial(1), ..., factorial(9)
 private static int[] FACTORIAL = {1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880};
 
 private static int factorialDigitSum(int x) {
  int sum = 0;
  while (x != 0) {
   sum += FACTORIAL[x % 10];
   x /= 10;
  }
  return sum;
 }
 
}