Problem 20 (Factorial digit sum)

Problem 20 (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!

 

In Python:

# Power digit sum
import time

startTime = time.time()

def factorial(n):
    if n == 1:
        return 1
    else:
        return n * factorial(n-1)

strNum = str(factorial(100))
numList = [int(num) for num in strNum]
print(sum(numList))
print(time.time() - startTime, "seconds")

Run time: 0.0001990795135498047 seconds

 

In Java:

//Euler20 Factorial digit sum
package project_euler11_20;

import java.math.BigInteger;

public class Euler20 {
	public static BigInteger factorial(BigInteger n) {
		if (n.compareTo(BigInteger.valueOf(1)) == 0) {
			return BigInteger.valueOf(1);
		} else {
			return n.multiply(factorial(n.subtract(BigInteger.valueOf(1))));
		}
	}
	public static void main(String[] args) {
		long startTime = System.currentTimeMillis();
		int sum = 0;
		BigInteger num = factorial(BigInteger.valueOf(100));
		String numString = num.toString();
		for (int i = 0; i < numString.length(); i++) {
			sum += Integer.parseInt(numString.charAt(i) + "");
		}
		System.out.println(sum);
		long endTime = System.currentTimeMillis();
		System.out.println((double)(endTime - startTime) / (double)1000 + "seconds");
	}
}

Run time: 0.004seconds

 

Solution: 648