Function Problem20

project_euler/problem_20/problem20.go:18–25

(input int)

import "math/big"

func Problem20(input int) int {
	factorial := bigFactorial(input)
	sum := 0
	for _, digit := range factorial.String() {
		sum += int(digit - '0')
	}
	return sum
}

// bigFactorial returns the factorial of n as a big.Int
// Use big package to handle large numbers