aoc2024/day-10/internal/one/solve.go

package one

import (
	"bytes"

	log "github.com/sirupsen/logrus"

	"github.com/onyx-and-iris/aoc2024/day-10/internal/queue"
)

const target = '9'

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

	var totalScore int
	queue := queue.New[point]()
	for _, pos := range graph.startPositions {
		if graph.isOutOfBounds(pos) {
			continue
		}
		queue.Enqueue(pos)

		var score int
		visited := make(map[point]struct{})
		endpoints := make(map[point]struct{})
		for !queue.IsEmpty() {
			current := queue.Dequeue()

			_, ok := endpoints[current]
			if ok {
				continue
			}
			endpoints[current] = struct{}{}

			if graph.valueAt(current) == target {
				score++
				continue
			}

			_, ok = visited[current]
			if ok {
				continue
			}
			visited[current] = struct{}{}

			for _, n := range neighbours(current) {
				if graph.isOutOfBounds(n) {
					continue
				}

				if graph.valueAt(n)-graph.valueAt(current) == 1 {
					log.Tracef("pushing %v with value %s back onto the queue\n", n, string(graph.valueAt(n)))
					queue.Enqueue(n)
				}
			}
		}

		log.Debugf("score for trailhead %v - %d\n", pos, score)
		totalScore += score
	}

	return totalScore, nil
}