Day 20 solution
Part 1 was pretty much just day 18 again, but without doors and with an input data parsing skill check. I simplified day 18 and went with a basic Dijkstra algorithm after the DFS to crawl the maze which solved this just fine. Part 2 messed me up more than I was expecting. The key feature for part 2 is changing up what the Dijkstra solver views as an "adjacent" node and injecting the appropriate depth as we traverse inner/outer portals. The main thing that tripped me up here from part 1 was that I needed to be carrying more data along with portals than just their locations, and I could no longer get away with storing the portals as pairs of their inner/outer locations, so a small refactor was needed. Once I made those corrections, it was mostly a matter of ironing out the "get neighbors" function to adhere to part 2's rules, which took me a lot of debugging to get just right. Part 2 still took me longer than I'd care to admit. I had problems wrapping my head around the problem.
This commit is contained in:
398
days/20.go
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398
days/20.go
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@ -0,0 +1,398 @@
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package days
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import (
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"container/heap"
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"fmt"
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"math"
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"strings"
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u "parnic.com/aoc2019/utilities"
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)
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type day20Cell int8
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type day20Graph map[day20Portal][]u.Pair[day20Portal, int]
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const (
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day20CellWall day20Cell = iota
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day20CellPath
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day20CellDonutHole
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)
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var (
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day20AdjacentOffsets = []u.Vec2i{
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{X: -1, Y: 0},
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{X: 1, Y: 0},
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{X: 0, Y: -1},
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{X: 0, Y: 1},
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}
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entrancePortal = day20Portal{name: "AA"}
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exitPortal = day20Portal{name: "ZZ"}
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)
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type day20Portal struct {
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name string
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inner bool
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depth int
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}
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type Day20 struct {
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grid [][]day20Cell
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entrance u.Vec2i
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exit u.Vec2i
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portals map[day20Portal]u.Vec2i
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portalNames []string
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}
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func (d *Day20) Parse() {
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d.portals = make(map[day20Portal]u.Vec2i)
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d.portalNames = make([]string, 0)
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lines := u.GetStringLines("20p")
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d.grid = make([][]day20Cell, len(lines)-4)
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currPortal := strings.Builder{}
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for row, line := range lines {
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y := row - 2
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isGridRow := row >= 2 && row < len(lines)-2
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if isGridRow {
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d.grid[y] = make([]day20Cell, len(line)-4)
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}
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for col, ch := range lines[row] {
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x := col - 2
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isGridCol := col >= 2 && col < len(line)-2
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if isGridRow && isGridCol {
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if ch == '#' {
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d.grid[y][x] = day20CellWall
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} else if ch == '.' {
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d.grid[y][x] = day20CellPath
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} else {
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d.grid[y][x] = day20CellDonutHole
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}
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}
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if ch >= 'A' && ch <= 'Z' {
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portalX := 0
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portalY := 0
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if len(line) > col+1 && line[col+1] >= 'A' && line[col+1] <= 'Z' {
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currPortal.WriteRune(ch)
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currPortal.WriteRune(rune(line[col+1]))
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if len(line) > col+2 && line[col+2] == '.' {
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portalY = y
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portalX = x + 2
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} else if col-1 >= 0 && line[col-1] == '.' {
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portalY = y
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portalX = x - 1
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} else {
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panic("!")
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}
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} else if len(lines) > row+1 && lines[row+1][col] >= 'A' && lines[row+1][col] <= 'Z' {
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currPortal.WriteRune(ch)
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currPortal.WriteRune(rune(lines[row+1][col]))
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if len(lines) > row+2 && lines[row+2][col] == '.' {
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portalY = y + 2
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portalX = x
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} else if row-1 >= 0 && lines[row-1][col] == '.' {
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portalY = y - 1
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portalX = x
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} else {
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panic("!")
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}
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}
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if currPortal.Len() == 2 {
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portalName := currPortal.String()
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portalVec := u.Vec2i{X: portalX, Y: portalY}
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if portalName == entrancePortal.name {
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d.entrance = portalVec
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} else if portalName == exitPortal.name {
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d.exit = portalVec
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} else {
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portal := day20Portal{
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name: portalName,
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inner: !d.isOuterPortal(portalVec),
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}
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d.portals[portal] = portalVec
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u.AddToArray(&d.portalNames, portalName)
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}
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currPortal.Reset()
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}
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}
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}
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}
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}
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func (d Day20) Num() int {
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return 20
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}
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func (d Day20) isPortal(vec u.Vec2i) (bool, int) {
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if d.grid[vec.Y][vec.X] != day20CellPath {
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return false, 0
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}
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for i, name := range d.portalNames {
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p, exists := d.portals[day20Portal{name: name, inner: !d.isOuterPortal(vec)}]
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if exists && vec == p {
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return true, i
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}
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}
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return false, 0
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}
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func (d Day20) Draw() {
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for y := range d.grid {
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for x := range d.grid[y] {
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switch d.grid[y][x] {
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case day20CellWall:
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fmt.Print("█")
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case day20CellDonutHole:
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fmt.Print(" ")
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case day20CellPath:
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posVec := u.Vec2i{X: x, Y: y}
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if posVec == d.entrance {
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fmt.Print("@")
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} else if posVec == d.exit {
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fmt.Print("!")
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} else {
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isPortal, portalIdx := d.isPortal(posVec)
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if isPortal {
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ch := 'a' + portalIdx
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if ch > 'z' {
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ch = 'A' + (portalIdx - 26)
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}
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fmt.Printf("%c", ch)
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} else {
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fmt.Print(" ")
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}
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}
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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 (d Day20) isOuterPortal(pos u.Vec2i) bool {
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return pos.X == 0 || pos.Y == 0 || pos.X == len(d.grid[0])-1 || pos.Y == len(d.grid)-1
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}
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func (d Day20) findAdjacentCells(inPos u.Vec2i) []u.Pair[day20Portal, int] {
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found := make([]u.Pair[day20Portal, int], 0)
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getAdjacent := func(pos u.Vec2i) []u.Vec2i {
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retAdjacent := make([]u.Vec2i, 0, len(day20AdjacentOffsets))
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for _, off := range day20AdjacentOffsets {
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offVec := u.Vec2i{X: pos.X + off.X, Y: pos.Y + off.Y}
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if offVec.Y < 0 || offVec.Y >= len(d.grid) || offVec.X < 0 || offVec.X >= len(d.grid[0]) {
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continue
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}
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if d.grid[offVec.Y][offVec.X] != day20CellPath {
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continue
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}
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retAdjacent = append(retAdjacent, offVec)
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}
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return retAdjacent
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}
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queue := make([]u.Pair[int, u.Vec2i], 0)
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visited := map[u.Vec2i]bool{
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inPos: true,
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}
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for _, adjacent := range getAdjacent(inPos) {
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queue = append(queue, u.Pair[int, u.Vec2i]{First: 1, Second: adjacent})
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}
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for len(queue) > 0 {
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next := queue[0]
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queue = queue[1:]
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if _, exists := visited[next.Second]; !exists {
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visited[next.Second] = true
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adjacentIsPortal, portalIdx := d.isPortal(next.Second)
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if adjacentIsPortal || next.Second == d.entrance || next.Second == d.exit {
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var portalName string
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if next.Second == d.entrance {
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portalName = entrancePortal.name
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} else if next.Second == d.exit {
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portalName = exitPortal.name
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} else {
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portalName = d.portalNames[portalIdx]
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}
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alreadyFound := false
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for _, p := range found {
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if p.First.name == portalName {
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alreadyFound = true
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break
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}
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}
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if !alreadyFound {
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found = append(found, u.Pair[day20Portal, int]{First: day20Portal{
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name: portalName,
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inner: !d.isOuterPortal(next.Second),
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}, Second: next.First})
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continue
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}
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}
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for _, neighbor := range getAdjacent(next.Second) {
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if _, exists := visited[neighbor]; !exists {
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queue = append(queue, u.Pair[int, u.Vec2i]{First: next.First + 1, Second: neighbor})
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}
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}
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}
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}
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return found
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}
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type day20PriorityQueue struct {
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distance int
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neighbor day20Portal
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}
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type day20PriorityQueueHeap []day20PriorityQueue
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func (h day20PriorityQueueHeap) Len() int { return len(h) }
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func (h day20PriorityQueueHeap) Less(i, j int) bool { return h[i].distance < h[j].distance }
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func (h day20PriorityQueueHeap) Swap(i, j int) { h[i], h[j] = h[j], h[i] }
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func (h *day20PriorityQueueHeap) Push(x any) {
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*h = append(*h, x.(day20PriorityQueue))
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}
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func (h *day20PriorityQueueHeap) Pop() any {
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old := *h
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n := len(old)
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x := old[n-1]
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*h = old[0 : n-1]
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return x
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}
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func (d Day20) dijkstra(graph day20Graph, start, end day20Portal, neighborFunc func(inPortal day20Portal) []u.Pair[day20Portal, int]) int {
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distance := make(map[day20Portal]int)
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ih := day20PriorityQueueHeap{
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day20PriorityQueue{
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distance: 0,
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neighbor: start,
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},
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}
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heap.Init(&ih)
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visited := make(map[day20Portal]bool)
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for ih.Len() > 0 {
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node := heap.Pop(&ih).(day20PriorityQueue)
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if node.neighbor == end {
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return node.distance
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}
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if _, exists := visited[node.neighbor]; exists {
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continue
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}
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visited[node.neighbor] = true
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for _, p := range neighborFunc(node.neighbor) {
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if _, exists := visited[p.First]; exists {
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continue
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}
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newDistance := node.distance + p.Second
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if dist, exists := distance[p.First]; !exists || newDistance < dist {
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distance[p.First] = newDistance
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heap.Push(&ih, day20PriorityQueue{
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distance: newDistance,
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neighbor: p.First,
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})
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}
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}
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}
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return math.MaxInt
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}
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func (d Day20) buildGraph() day20Graph {
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graph := make(day20Graph, len(d.portals)+1)
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adjacent := d.findAdjacentCells(d.entrance)
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graph[entrancePortal] = adjacent
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for portal, portalVec := range d.portals {
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adjacent = d.findAdjacentCells(portalVec)
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graph[portal] = adjacent
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}
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return graph
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}
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func (d Day20) getDepthNeighbors(graph day20Graph, portal day20Portal) []u.Pair[day20Portal, int] {
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basePortal := portal
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basePortal.depth = 0
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baseNeighbors := graph[basePortal]
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neighbors := make([]u.Pair[day20Portal, int], 0)
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if portal.inner {
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n := day20Portal{name: portal.name, inner: false, depth: portal.depth + 1}
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neighbors = append(neighbors, u.Pair[day20Portal, int]{First: n, Second: 1})
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}
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if portal.depth == 0 {
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for _, i := range baseNeighbors {
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if i.First.inner || i.First.name == entrancePortal.name || i.First.name == exitPortal.name {
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neighbors = append(neighbors, u.Pair[day20Portal, int]{First: i.First, Second: i.Second})
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}
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}
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} else {
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if !portal.inner {
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n := day20Portal{name: portal.name, inner: true, depth: portal.depth - 1}
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neighbors = append(neighbors, u.Pair[day20Portal, int]{First: n, Second: 1})
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}
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for _, i := range baseNeighbors {
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if i.First.name != entrancePortal.name && i.First.name != exitPortal.name {
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n := day20Portal{name: i.First.name, inner: i.First.inner, depth: portal.depth}
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neighbors = append(neighbors, u.Pair[day20Portal, int]{First: n, Second: i.Second})
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}
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}
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}
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return neighbors
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}
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func (d *Day20) Part1() string {
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// d.Draw()
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graph := d.buildGraph()
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for portal, adjacent := range graph {
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if portal.name == entrancePortal.name {
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continue
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}
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graph[portal] = append(adjacent, u.Pair[day20Portal, int]{First: day20Portal{name: portal.name, inner: !portal.inner}, Second: 1})
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}
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distance := d.dijkstra(graph, entrancePortal, exitPortal, func(inPortal day20Portal) []u.Pair[day20Portal, int] { return graph[inPortal] })
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return fmt.Sprintf("Steps to traverse maze: %s%d%s", u.TextBold, distance, u.TextReset)
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}
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func (d *Day20) Part2() string {
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graph := d.buildGraph()
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distance := d.dijkstra(graph, entrancePortal, exitPortal, func(inPortal day20Portal) []u.Pair[day20Portal, int] { return d.getDepthNeighbors(graph, inPortal) })
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return fmt.Sprintf("Steps to traverse recursive maze: %s%d%s", u.TextBold, distance, u.TextReset)
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}
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