# [Golang] Power digit sum - Problem 16 - Project Euler

Problem: [1]

215 = 32768 and the sum of its digits is 3 + 2 + 7 + 6 + 8 = 26.

What is the sum of the digits of the number 21000?

Solution:

We use large number addition [2] and the following formula:

2n = 2n − 1 + 2n − 1

The result is:

21000 = 10715086071862673209484250490600018105614048117055336074437503883703510511249361224931983788156958581275946729175531468251871452856923140435984577574698574803934567774824230985421074605062371141877954182153046474983581941267398767559165543946077062914571196477686542167660429831652624386837205668069376

sum of digits = 1366

Run Code on Go Playground

```package main

import (
"fmt"
)

const MaxDigits = 350
const BASE = 10

func MakePositiveInt(s string) (n [MaxDigits]int) {
// make n zero
for i := 0; i < MaxDigits; i++ {
n[i] = 0
}

for index, digit := range s {
i := len(s) - index - 1
switch digit {
case '0':
n[i] = 0
case '1':
n[i] = 1
case '2':
n[i] = 2
case '3':
n[i] = 3
case '4':
n[i] = 4
case '5':
n[i] = 5
case '6':
n[i] = 6
case '7':
n[i] = 7
case '8':
n[i] = 8
case '9':
n[i] = 9
default:
panic("invalid digit in number string")
}
}

return
}

func AddPositiveInt(a, b [MaxDigits]int) (c [MaxDigits]int) {
var carry, sum = 0, 0

// make c zero
for i := 0; i < MaxDigits; i++ {
c[i] = 0
}

for i := 0; i < MaxDigits; i++ {
sum = a[i] + b[i] + carry

if sum >= BASE {
carry = 1
sum -= BASE
} else {
carry = 0
}

c[i] = sum
}

if carry != 0 {
}

return
}

func PrintPositiveInt(a [MaxDigits]int) {
for i := MaxDigits - 1; i >= 0; i-- {
if isLeadingZero && a[i] == 0 {
continue
} else {
fmt.Print(a[i])
}
}
fmt.Println("\n")
}

func main() {
result := MakePositiveInt("2")

for i := 1; i < 1000; i++ {
}
PrintPositiveInt(result)

sum := 0
for i := 0; i < MaxDigits; i++ {
sum += result[i]
}
fmt.Println(sum)
}
```

Tested on: Go Playground

References: