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

package one

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
	}

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

		stack, ok := explore(graph, graph.robot, directions(dir), newStack())
		if !ok {
			log.Debug("path ends with '#', continuing...")
			continue
		}

		for !stack.IsEmpty() {
			point := stack.Pop().(point)
			graph.updateBox(point, directions(dir))
		}
		graph.updateRobot(directions(dir))

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

	var sum int
	for box := range graph.boxes {
		sum += (100 * box.y) + box.x
	}

	return sum, nil
}

func explore(graph *graph, next point, direction direction, stack *stack) (*stack, bool) {
	ns := neighbours(next)

	log.Debug(string(graph.valueAt(ns[direction])))

	switch graph.valueAt(ns[direction]) {
	case '#':
		return nil, false
	case '.':
		return stack, true
	case 'O':
		stack.Push(ns[direction])
	}

	return explore(graph, ns[direction], direction, stack)
}