aoc2024/day-15/internal/two/solve.go

package two

import (
	"bytes"

	log "github.com/sirupsen/logrus"
)

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

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

	for _, dir := range dirs {
		log.Debugf("about to explore '%s' direction from robot location (%s)", string(dir), graph.robot.String())

		switch directions(dir) {
		case N, S:
			exploreNorthSouth(directions(dir), graph)
		case W, E:
			exploreWestEast(directions(dir), graph)
		}

		log.Debugf("\n%s\n", graph.String())
	}

	var sum int
	for y, line := range graph.data {
		for x, r := range line {
			if r == '[' {
				sum += (100 * y) + x
			}
		}
	}

	return sum, nil
}

func exploreWestEast(direction direction, g *graph) {
	stack := newStack()
	if ok := exploreDFS(g, g.robot, direction, stack); !ok {
		log.Debug("path ends with '#', continuing...")
		return
	}

	for !stack.IsEmpty() {
		point := stack.Pop().(point)
		g.updateBox(point, direction)
	}
	g.updateRobot(direction)
}

func exploreNorthSouth(direction direction, g *graph) {
	om, ok := exploreBFS(g, direction)

	if ok {
		for pair := om.Newest(); pair != nil; pair = pair.Prev() {
			g.updateBox(pair.Key, direction)
		}
		g.updateRobot(direction)
	}
}