aoc2024/day-16/internal/two/graph.go

package two

import (
	hp "container/heap"
	"math"
	"slices"
	"strings"

	log "github.com/sirupsen/logrus"
)

type graph struct {
	start node
	end   node
	data  []string
}

func newGraph() *graph {
	return &graph{}
}

func (g *graph) String() string {
	return strings.Join(g.data, "\n")
}

func (g *graph) valueAt(n node) rune {
	return rune(g.data[n.y][n.x])
}

func (g *graph) dijkstra() int {
	heap := newHeap()
	hp.Push(heap, move{g.start, 0, []node{g.start}})
	visited := make(map[node]int)
	const turnCost int = 1000
	lowestCost := math.MaxInt

	bestPaths := [][]node{}
	for heap.Len() > 0 {
		current := hp.Pop(heap).(move)

		// we're on a path that's already exceeded the lowest cost
		if current.cost > lowestCost {
			continue
		}

		if g.valueAt(current.node) == 'E' {
			bestPaths = append(bestPaths, current.path)
			lowestCost = current.cost
			continue
		}

		if v, ok := visited[current.node]; ok {
			if v < current.cost {
				continue
			}
		}
		visited[current.node] = current.cost

		for _, n := range neighbours(current.node) {
			if g.valueAt(current.node) == '#' {
				continue
			}

			next_cost := current.cost + 1
			if n.direction != current.node.direction {
				next_cost += turnCost
			}

			hp.Push(heap, newMove(n, next_cost, append(slices.Clone(current.path), n)))
		}
	}

	possibleSafe := make(map[coords]struct{})
	for _, path := range bestPaths {
		for _, n := range path {
			possibleSafe[n.coords] = struct{}{}
		}
	}

	log.Debugf("\n%s\n", g.debug(possibleSafe))

	return len(possibleSafe)
}

func (g *graph) debug(possibleSafe map[coords]struct{}) string {
	temp := slices.Clone(g.data)
	for n := range possibleSafe {
		temp[n.y] = replaceAtIndex(temp[n.y], 'O', n.x)
	}
	return strings.Join(temp, "\n")
}