aoc2024/day-03/internal/two/solve.go

package two

import (
	"bufio"
	"bytes"
	"io"
	"regexp"

	log "github.com/sirupsen/logrus"
)

var reMulOrDoOrDont = regexp.MustCompile(`mul\(([0-9]{1,3}),([0-9]{1,3})\)|do\(\)|don't\(\)`)

func Solve(buf []byte) (int, error) {
	r := bytes.NewReader(buf)
	sum, err := parseLines(r)
	if err != nil {
		return 0, err
	}

	return sum, nil
}

func parseLines(r io.Reader) (int, error) {
	var sum int
	var do bool = true

	scanner := bufio.NewScanner(r)
	for scanner.Scan() {
		matches := reMulOrDoOrDont.FindAllStringSubmatch(scanner.Text(), -1)
		for _, m := range matches {
			switch m[0] {
			case "do()":
				do = true
				log.Debug("hit a do")
			case "don't()":
				do = false
				log.Debug("hit a don't")
			}

			if do {
				if m[1] != "" && m[2] != "" {
					log.Debugf("%s * %s\n", m[1], m[2])
					sum += mustConv(m[1]) * mustConv(m[2])
				}
			}
		}
	}

	if err := scanner.Err(); err != nil {
		return 0, err
	}

	return sum, nil
}