Problem #20

Problem link
Solution:

package main

import (
    "big"
    "strconv"
)

func main() {
    mul := big.NewInt(1)
    for i := 2; i <= 100; i++ {
        mul.Mul(mul, big.NewInt(int64(i)))
    }
    result, digit := 0, 0
    for i := range mul.String() {
        digit, _ = strconv.Atoi(string(mul.String()[i]))
        result += digit
    }
    println(result)
}

Result: 648
Time: 0m0.023s