Problem #16

Problem link
Solution:

package main

import (
    "strconv"
)

func main() {
    input := "2"
    for i := 0; i < 999; i++ {
        input = multipyByTwo(input)
    }
    println(sumUpDigits(input))
}

func sumUpDigits(input string) int {
    result, digit := 0, 0
    for i := range input {
        digit, _ = strconv.Atoi(string(input[i]))
        result += digit
    }
    return result
}

func multipyByTwo(input string) string {
    result, carryout, digit := "", 0, 0
    for i := len(input) - 1; i >= 0; i-- {
        digit, _ = strconv.Atoi(string(input[i]))
        digit = digit*2 + carryout
        carryout = digit / 10
        digit = digit % 10
        result = strconv.Itoa(digit) + result
    }
    if carryout > 0 {
        result = strconv.Itoa(carryout) + result
    }
    return result
}

Result: 1366
Time: 0m0.228s