Advent of Code 2023 day 1

main.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"regexp"
	"strconv"
)

var lineRe = regexp.MustCompile(`\d|one|two|three|four|five|six|seven|eight|nine`)

var numbers = map[string]uint64{
	"one":   1,
	"two":   2,
	"three": 3,
	"four":  4,
	"five":  5,
	"six":   6,
	"seven": 7,
	"eight": 8,
	"nine":  9,
}

func parseNumber(digitStr string) uint64 {
	digit, exists := numbers[digitStr]
	if !exists {
		digit, _ = strconv.ParseUint(digitStr, 10, 8)
	}
	return digit
}

func lineToNumber(line string) uint64 {
	first := lineRe.FindStringIndex(line)
	last := first
	for last[0]+1 < len(line) {
		match := lineRe.FindStringIndex(line[last[0]+1:])
		if match == nil {
			break
		}
		last = []int{match[0] + last[0] + 1, match[1] + last[0] + 1}
	}
	digit1 := parseNumber(line[first[0]:first[1]])
	digit2 := parseNumber(line[last[0]:last[1]])
	return 10*digit1 + digit2
}

func main() {
	if len(os.Args) != 2 {
		fmt.Println("Expected input file name to be passed in as an argument")
		return
	}
	readFile, err := os.Open(os.Args[1])

	if err != nil {
		fmt.Println(err)
	}

	fileScanner := bufio.NewScanner(readFile)
	fileScanner.Split(bufio.ScanLines)

	sum := uint64(0)
	for fileScanner.Scan() {
		sum += lineToNumber(fileScanner.Text())
	}

	fmt.Println(sum)
	readFile.Close()
}