adventofcode/2024/day16/main.go

package main

import (
	"fmt"
	"math"

	h "git.bullercodeworks.com/brian/adventofcode/helpers"
)

func main() {
	inp := h.StdinToCoordMap()
	start, _ := inp.FindFirst('S')
	end, _ := inp.FindFirst('E')

	score, seats := bfs(inp, start, end)
	fmt.Println("# Part 1")
	fmt.Println("Minimum Score:", score)
	fmt.Println("# Part 2")
	fmt.Println("Best Seats:", seats)
}

func bfs(inp h.CoordByteMap, s, e h.Coordinate) (int, int) {
	start := CD{c: s, d: E}
	minScore := math.MaxInt
	queue := []State{
		{
			pos:  start,
			path: []h.Coordinate{},
		},
	}
	visited := make(map[CD]int)
	sizeToC := make(map[int][]h.Coordinate)

	for len(queue) > 0 {
		currState := queue[0]
		queue = queue[1:]

		if currState.score > minScore {
			continue
		}

		if currState.pos.c.Equals(e) {
			if currState.score <= minScore {
				minScore = currState.score
				sizeToC[minScore] = append(sizeToC[minScore], currState.path...)
			}
			continue
		}

		for _, n := range currState.pos.GetNeighbors() {
			if inp.Get(n.c) == '#' {
				continue
			}
			score := currState.score + 1
			if currState.pos.d != n.d {
				score += 1000
			}
			if prev, ok := visited[n]; ok {
				if prev < score {
					continue
				}
			}
			visited[n] = score

			np := make([]h.Coordinate, len(currState.path))
			copy(np, currState.path)
			queue = append(queue, State{
				pos:   n,
				path:  append(np, n.c),
				score: score,
			})
		}
	}
	seatMap := make(map[h.Coordinate]bool)
	for _, p := range sizeToC[minScore] {
		seatMap[p] = true
	}
	/*
		for y := inp.TLY; y <= inp.BRY; y++ {
			for x := inp.TLX; x <= inp.BRX; x++ {
				c := h.Coordinate{X: x, Y: y}
				if _, ok := seatMap[c]; ok {
					fmt.Print("O")
				} else {
					fmt.Print(string(inp.Get(c)))
				}
			}
			fmt.Println()
		}
	*/
	return minScore, len(seatMap) + 1
}

var (
	N    = h.Coordinate{X: 0, Y: -1}
	E    = h.Coordinate{X: 1, Y: 0}
	S    = h.Coordinate{X: 0, Y: 1}
	W    = h.Coordinate{X: -1, Y: 0}
	Dirs = []h.Coordinate{N, E, S, W}
)

type CD struct {
	c, d h.Coordinate
}

func (cd CD) GetNeighbors() []CD {
	var ret []CD
	opp := h.Coordinate{X: -cd.d.X, Y: -cd.d.Y}
	for _, dir := range Dirs {
		if !dir.Equals(opp) {
			ret = append(ret, CD{
				c: cd.c.Add(dir),
				d: dir,
			})
		}
	}
	return ret
}

type State struct {
	pos   CD
	path  []h.Coordinate
	score int
}