aoc2024/day-23/internal/two/solve.go

package two

import (
	"bytes"
	"slices"
	"strings"
	"sync"

	"github.com/onyx-and-iris/aoc2024/day-23/internal/set"
	log "github.com/sirupsen/logrus"
)

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

	networks := make(map[string]*set.Set)
	nodes := set.New()
	for _, connection := range connections {
		if _, found := networks[connection[0]]; !found {
			networks[connection[0]] = set.New()
		}
		networks[connection[0]].Add(connection[1])

		if _, found := networks[connection[1]]; !found {
			networks[connection[1]] = set.New()
		}
		networks[connection[1]].Add(connection[0])

		nodes.Add(connection[0])
		nodes.Add(connection[1])
	}

	cliquesChan := make(chan clique)
	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
		defer wg.Done()
		next([]string{}, nodes, set.New(), cliquesChan, networks)
	}()

	go func() {
		wg.Wait()
		close(cliquesChan)
	}()

	var maxLen int
	var maxLenClique []string
	for c := range cliquesChan {
		if c.Len() > maxLen {
			maxLen = c.Len()
			maxLenClique = c.sorted()
			log.Debug(c)
		}
	}

	return strings.Join(maxLenClique, ","), nil
}

func next(
	R []string,
	P, X *set.Set,
	cliquesChan chan<- clique,
	networks map[string]*set.Set,
) {
	if P.Size() == 0 && X.Size() == 0 {
		cliquesChan <- clique{slices.Clone(R)}
		return
	}

	for _, v := range P.List() {
		next(append(R, v), P.Intersection(networks[v]), X.Intersection(networks[v]), cliquesChan, networks)

		P.Remove(v)
		X.Add(v)
	}
}