package main

import (
	"fmt"
	"regexp"
	"strconv"
)

// one takes a string array and for each line:
// Combine the first digit and the last digit (in that order) to form a single two-digit number.
// Returns the sum of all calibrated values.
func one(lines []string) (int, error) {
	re := regexp.MustCompile(`\d`)

	sum := 0
	for _, line := range lines {
		m := re.FindAllString(line, -1)
		if len(m) > 0 {
			num, err := strconv.Atoi(fmt.Sprintf("%s%s", m[0], m[len(m)-1]))
			if err != nil {
				return 0, err
			}
			sum += num
		}
	}
	return sum, nil
}