aoc2024/day-18/internal/one/solve.go

package one

import (
	"bytes"
	"math"

	"github.com/onyx-and-iris/aoc2024/day-18/internal/config"
	"github.com/onyx-and-iris/aoc2024/day-18/internal/queue"
	log "github.com/sirupsen/logrus"
)

var ShortestPath []Point

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

	log.Debugf("start: %v end: %v", graph.start, graph.end)

	log.Debugf("\n%s\n", graph.String())
	queue := queue.New[Point]()
	queue.Enqueue(graph.start)
	visited := make(map[Point]struct{})
	costs := make(map[Point]int)
	prev := make(map[Point]Point)

	for !queue.IsEmpty() {
		current := queue.Dequeue()

		if current == graph.end {
			break
		}

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

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

			if graph.valueAt(n) == '#' {
				continue
			}

			_, ok := costs[n]
			if !ok {
				costs[n] = math.MaxInt
			}

			new_cost := costs[current] + 1
			if new_cost < costs[n] {
				costs[n] = new_cost
				prev[n] = current
				queue.Enqueue(n)
			}
		}
	}

	ShortestPath = []Point{graph.end}
	node := prev[graph.end]
	for node != graph.start {
		ShortestPath = append(ShortestPath, prev[node])
		node = prev[node]
	}

	log.Debugf("\n%s\n", graph.debug(ShortestPath))

	return len(ShortestPath), nil
}