Solve day 16 part 1
parent
5f5ec795e7
commit
34d2d7533e
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@ -0,0 +1,310 @@
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package main
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import (
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"errors"
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"fmt"
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"io"
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"os"
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"slices"
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"strings"
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)
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type Tile rune
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const (
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TileMirrorRight Tile = '/'
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TileMirrorLeft Tile = '\\'
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TileSplitterVertical Tile = '|'
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TileSplitterHorizontal Tile = '-'
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)
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type Direction int
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const (
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DirectionNorth Direction = iota
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DirectionEast
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DirectionSouth
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DirectionWest
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)
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type Coordinate struct {
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row int
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col int
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}
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type Beam struct {
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position Coordinate
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direction Direction
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}
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type TileGrid struct {
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height int
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width int
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tiles map[Coordinate]Tile
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}
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func (dir Direction) Horizontal() bool {
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return dir == DirectionEast || dir == DirectionWest
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}
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func (dir Direction) Vertical() bool {
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return dir == DirectionNorth || dir == DirectionSouth
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}
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func (grid TileGrid) Print() {
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grid.PrintWithBeams(nil)
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}
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func (grid TileGrid) PrintWithBeams(beams []Beam) {
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for row := 0; row < grid.height; row++ {
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for col := 0; col < grid.width; col++ {
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position := Coordinate{row: row, col: col}
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tile, ok := grid.tiles[position]
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beamIdx := slices.IndexFunc(beams, func(beam Beam) bool {
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return beam.position == position
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})
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if beamIdx != -1 && !ok {
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beamAtPosition := beams[beamIdx]
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switch beamAtPosition.direction {
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case DirectionNorth:
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fmt.Print("^")
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case DirectionSouth:
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fmt.Print("v")
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case DirectionWest:
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fmt.Print("<")
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case DirectionEast:
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fmt.Print(">")
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default:
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panic(fmt.Sprintf("invalid direction %d", beamAtPosition.direction))
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}
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} else if !ok {
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fmt.Print(".")
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} else {
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fmt.Printf("%c", tile)
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}
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}
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fmt.Println()
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}
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}
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func (grid TileGrid) InBounds(position Coordinate) bool {
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return position.row >= 0 && position.col >= 0 && position.row < grid.height && position.col < grid.width
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}
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func (beam Beam) MovedInDirection(dir Direction) Beam {
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updPosition := beam.position
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switch dir {
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case DirectionNorth:
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updPosition.row--
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case DirectionSouth:
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updPosition.row++
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case DirectionEast:
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updPosition.col++
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case DirectionWest:
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updPosition.col--
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default:
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panic(fmt.Sprintf("invalid direction value %d", dir))
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}
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return Beam{
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position: updPosition,
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direction: dir,
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}
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}
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func (beam Beam) RotatedInDirection(dir Direction) Beam {
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return Beam{
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position: beam.position,
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direction: dir,
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}
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}
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func main() {
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if len(os.Args) != 2 && len(os.Args) != 3 {
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fmt.Fprintf(os.Stderr, "Usage: %s inputfile\n", os.Args[0])
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os.Exit(1)
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}
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inputFilename := os.Args[1]
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inputFile, err := os.Open(inputFilename)
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if err != nil {
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panic(fmt.Sprintf("could not open input file: %s", err))
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}
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defer inputFile.Close()
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inputBytes, err := io.ReadAll(inputFile)
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if err != nil {
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panic(fmt.Sprintf("could not read input file: %s", err))
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}
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input := strings.TrimSpace(string(inputBytes))
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inputLines := strings.Split(input, "\n")
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grid, err := parseTileGrid(inputLines)
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if err != nil {
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panic(fmt.Sprintf("failed to parse input: %s", err))
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}
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// grid.Print()
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fmt.Printf("Part 1: %d\n", part1(grid))
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}
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func part1(grid TileGrid) int {
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startingBeam := Beam{position: Coordinate{row: 0, col: 0}, direction: DirectionEast}
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beams := []Beam{startingBeam}
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nextBeams := []Beam{}
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beamHistory := map[Beam]struct{}{
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startingBeam: {},
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}
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for len(beams) > 0 {
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for _, beam := range beams {
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updBeam := beam.MovedInDirection(beam.direction)
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tile, ok := grid.tiles[updBeam.position]
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if ok {
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resultingBeams := beamsFromCollision(tile, updBeam)
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nextBeams = append(nextBeams, resultingBeams...)
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} else {
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nextBeams = append(nextBeams, updBeam)
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}
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}
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beams = []Beam{}
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for _, beam := range nextBeams {
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_, seenBeam := beamHistory[beam]
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if grid.InBounds(beam.position) && !seenBeam {
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beams = append(beams, beam)
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beamHistory[beam] = struct{}{}
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}
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}
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nextBeams = []Beam{}
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}
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visitedPositions := map[Coordinate]struct{}{}
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for beam := range beamHistory {
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visitedPositions[beam.position] = struct{}{}
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}
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return len(visitedPositions)
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}
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func beamsFromCollision(tile Tile, beam Beam) []Beam {
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switch tile {
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case TileMirrorLeft, TileMirrorRight:
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return beamsFromMirror(tile, beam)
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case TileSplitterHorizontal, TileSplitterVertical:
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return beamsFromSplitter(tile, beam)
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default:
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panic(fmt.Sprintf("invalid tile %c", tile))
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}
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}
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func beamsFromSplitter(tile Tile, beam Beam) []Beam {
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if tile != TileSplitterHorizontal && tile != TileSplitterVertical {
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panic("cannot treat a non-splitter tile as a splitter")
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}
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if beam.direction.Horizontal() && tile == TileSplitterHorizontal {
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return []Beam{beam}
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} else if beam.direction.Vertical() && tile == TileSplitterVertical {
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return []Beam{beam}
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} else if beam.direction.Horizontal() && tile == TileSplitterVertical {
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return []Beam{
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beam.RotatedInDirection(DirectionNorth),
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beam.RotatedInDirection(DirectionSouth),
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}
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} else if beam.direction.Vertical() && tile == TileSplitterHorizontal {
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return []Beam{
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beam.RotatedInDirection(DirectionWest),
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beam.RotatedInDirection(DirectionEast),
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}
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} else {
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// This can't happen, we've hit all four permutations already
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panic("invalid configuration of beam")
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}
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}
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func beamsFromMirror(tile Tile, beam Beam) []Beam {
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switch tile {
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case TileMirrorRight:
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return beamsFromRightMirror(tile, beam)
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case TileMirrorLeft:
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return beamsFromLeftMirror(tile, beam)
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default:
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panic("cannot treat non-mirror as a mirror")
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}
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}
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func beamsFromRightMirror(tile Tile, beam Beam) []Beam {
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if tile != TileMirrorRight {
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panic("cannot treat non-right mirror as right mirror")
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}
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switch beam.direction {
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case DirectionEast:
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return []Beam{beam.RotatedInDirection(DirectionNorth)}
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case DirectionWest:
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return []Beam{beam.RotatedInDirection(DirectionSouth)}
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case DirectionNorth:
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return []Beam{beam.RotatedInDirection(DirectionEast)}
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case DirectionSouth:
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return []Beam{beam.RotatedInDirection(DirectionWest)}
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default:
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panic(fmt.Sprintf("invalid direction value %d", beam.direction))
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}
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}
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func beamsFromLeftMirror(tile Tile, beam Beam) []Beam {
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if tile != TileMirrorLeft {
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panic("cannot treat non-right mirror as right mirror")
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}
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switch beam.direction {
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case DirectionEast:
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return []Beam{beam.RotatedInDirection(DirectionSouth)}
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case DirectionWest:
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return []Beam{beam.RotatedInDirection(DirectionNorth)}
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case DirectionNorth:
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return []Beam{beam.RotatedInDirection(DirectionWest)}
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case DirectionSouth:
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return []Beam{beam.RotatedInDirection(DirectionEast)}
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default:
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panic(fmt.Sprintf("invalid direction value %d", beam.direction))
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}
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}
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func parseTileGrid(inputLines []string) (TileGrid, error) {
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if len(inputLines) == 0 {
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return TileGrid{}, fmt.Errorf("no tiles in grid")
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}
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width := len(inputLines[0])
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height := len(inputLines)
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tiles := make(map[Coordinate]Tile)
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for row, line := range inputLines {
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if len(line) != width {
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return TileGrid{}, errors.New("lines have unequal lengths")
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}
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for col, char := range line {
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switch char {
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case '.':
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continue
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case rune(TileMirrorLeft), rune(TileMirrorRight), rune(TileSplitterHorizontal), rune(TileSplitterVertical):
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pos := Coordinate{row: row, col: col}
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tiles[pos] = Tile(char)
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default:
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return TileGrid{}, fmt.Errorf("invalid tile character %c", char)
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}
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}
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}
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return TileGrid{
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height: height,
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width: width,
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tiles: tiles,
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}, nil
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}
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