aoc2024/day-19/internal/one/solve.go

package one

import (
	"bytes"
	"cmp"
	"slices"
	"strings"

	log "github.com/sirupsen/logrus"
)

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

	log.Debug(stripes, designs)

	var sum int
	for _, design := range designs {
		ok := isPossibleArrangement(design, stripes)
		if ok {
			log.Debugf("design: %s is possible", design)
			sum++
		}
	}

	return sum, nil
}

func isPossibleArrangement(design string, stripes []string) bool {
	if len(design) == 0 {
		return true
	}

	greedy := []string{}
	for _, stripe := range stripes {
		log.Debugf("testing design: %s with stripe: %s", design, stripe)
		if strings.HasPrefix(design, stripe) {
			log.Debugf("design: %s has prefix %s", design, stripe)

			greedy = append(greedy, stripe)
		}
	}

	slices.SortFunc(greedy, func(a, b string) int {
		return cmp.Compare(len(b), len(a))
	})

	for _, g := range greedy {
		if isPossibleArrangement(design[len(g):], stripes) {
			return true
		}
	}
	return false
}