258_add_digits.go

package main

import (
	"strconv"
)

func addDigits(num int) int {

	for len(strconv.Itoa(num)) > 1 {
		num = add(num)
	}

	return num
}

func add(num int) int {
	sum := 0
	for num > 0 {
		sum += num % 10
		num /= 10
	}
	return sum
}