Optimizations and minor cleanups

Thanks to Go's profiling tools, I discovered that the memoization, while it was cutting down runtime significantly, was itself slow because it was using arrays. Swapping those arrays out for maps made a _massive_ difference (4s/14s part1/part2 to 1ms/2ms with no other changes). Lesson learned. Again.

The IntHeap rename was long overdue since I took the code originally from Go's sample docs for priority queues.

days/17.go

@@ -0,0 +1,422 @@
+package days
+
+import (
+	"fmt"
+	"strings"
+
+	u "parnic.com/aoc2019/utilities"
+)
+
+type camViewCellType int
+type botFacing int
+type day17Grid [][]camViewCellType
+
+const (
+	cellTypeScaffold camViewCellType = iota
+	cellTypeOpen
+	cellTypeInvalid
+)
+
+const (
+	botFacingUp botFacing = iota
+	botFacingLeft
+	botFacingDown
+	botFacingRight
+
+	botFacingFirst = botFacingUp
+	botFacingLast  = botFacingRight
+)
+
+const (
+	dirLeft                 = 1
+	dirRight                = -1
+	maxInstructionSetLength = 20
+)
+
+var (
+	day17AdjacentOffsets = []u.Vec2i{
+		{X: -1, Y: 0},
+		{X: 1, Y: 0},
+		{X: 0, Y: -1},
+		{X: 0, Y: 1},
+	}
+)
+
+type Day17 struct {
+	program u.IntcodeProgram
+}
+
+func (d *Day17) Parse() {
+	d.program = u.LoadIntcodeProgram("17p")
+}
+
+func (d Day17) Num() int {
+	return 17
+}
+
+func (currentDir botFacing) getNewFacingDir(turnDir int) botFacing {
+	currentDir += botFacing(turnDir)
+	if currentDir < botFacingFirst {
+		currentDir = botFacingLast
+	} else if currentDir > botFacingLast {
+		currentDir = botFacingFirst
+	}
+
+	return currentDir
+}
+
+func (grid day17Grid) Draw(botLocation u.Vec2i, botFacingDir botFacing, endLocation u.Vec2i) {
+	for y := range grid {
+		for x := range grid[y] {
+			switch grid[y][x] {
+			case cellTypeOpen:
+				fmt.Print(" ")
+			case cellTypeScaffold:
+				char := "█"
+				color := u.ColorBlack
+				if botLocation.X == x && botLocation.Y == y {
+					switch botFacingDir {
+					case botFacingUp:
+						char = "^"
+					case botFacingLeft:
+						char = "<"
+					case botFacingDown:
+						char = "v"
+					case botFacingRight:
+						char = ">"
+					}
+				} else if endLocation.X == x && endLocation.Y == y {
+					char = "@"
+				} else {
+					color = u.ColorWhite
+				}
+				fmt.Printf("%s%s%s%s", u.BackgroundWhite, color, char, u.TextReset)
+			}
+		}
+		fmt.Println()
+	}
+}
+
+func (grid day17Grid) getAdjacentScaffolds(y, x int) []u.Vec2i {
+	retval := make([]u.Vec2i, 0)
+	for _, offset := range day17AdjacentOffsets {
+		offY := y + offset.Y
+		offX := x + offset.X
+		if offY < 0 || offY >= len(grid) ||
+			offX < 0 || offX >= len(grid[0]) {
+			continue
+		}
+
+		if grid[offY][offX] == cellTypeScaffold {
+			retval = append(retval, u.Vec2i{X: offX, Y: offY})
+		}
+	}
+
+	return retval
+}
+
+func (grid day17Grid) forEachCellOfType(t camViewCellType, f func(y, x int)) {
+	for y := range grid {
+		for x := range grid[y] {
+			if grid[y][x] == t {
+				f(y, x)
+			}
+		}
+	}
+}
+
+func (grid *day17Grid) processGridUpdate(y int, rVal rune, currBotLocation u.Vec2i, currBotFacing botFacing) (int, u.Vec2i, botFacing) {
+	grid.appendValue(rVal, y)
+
+	switch rVal {
+	case '\n':
+		y++
+	case '^', '<', 'v', '>':
+		currBotLocation = u.Vec2i{X: len((*grid)[y]) - 1, Y: y}
+		switch rVal {
+		case '^':
+			currBotFacing = botFacingUp
+		case '<':
+			currBotFacing = botFacingLeft
+		case 'v':
+			currBotFacing = botFacingDown
+		case '>':
+			currBotFacing = botFacingRight
+		}
+	}
+
+	return y, currBotLocation, currBotFacing
+}
+
+func (grid day17Grid) getCellTypeInDirection(y, x int, facingDir botFacing) (camViewCellType, int, int) {
+	newX := x
+	newY := y
+	switch facingDir {
+	case botFacingUp:
+		newY--
+	case botFacingLeft:
+		newX--
+	case botFacingDown:
+		newY++
+	case botFacingRight:
+		newX++
+	}
+
+	if newY < 0 || newY >= len(grid) || newX < 0 || newX >= len(grid[0]) {
+		return cellTypeInvalid, newY, newX
+	}
+
+	return grid[newY][newX], newY, newX
+}
+
+func (grid *day17Grid) appendValue(rVal rune, row int) {
+	ensureCapacity := func(y int) {
+		for len(*grid) <= y {
+			*grid = append(*grid, make([]camViewCellType, 0))
+		}
+	}
+
+	switch rVal {
+	case '#':
+		ensureCapacity(row)
+		(*grid)[row] = append((*grid)[row], cellTypeScaffold)
+	case '.':
+		ensureCapacity(row)
+		(*grid)[row] = append((*grid)[row], cellTypeOpen)
+	case '^', '<', 'v', '>':
+		ensureCapacity(row)
+		(*grid)[row] = append((*grid)[row], cellTypeScaffold)
+	}
+}
+
+func (grid day17Grid) findEndLocation(botLocation u.Vec2i) u.Vec2i {
+	var endLocation u.Vec2i
+	grid.forEachCellOfType(cellTypeScaffold, func(y, x int) {
+		if numSurrounding := len(grid.getAdjacentScaffolds(y, x)); numSurrounding == 1 {
+			if botLocation.X != x || botLocation.Y != y {
+				endLocation = u.Vec2i{X: x, Y: y}
+			}
+		}
+	})
+
+	return endLocation
+}
+
+func (grid day17Grid) getTurnDirectionFromCorner(pos u.Vec2i, botFacingDir botFacing) (int, string) {
+	adj := grid.getAdjacentScaffolds(pos.Y, pos.X)
+	turnDirection := 0
+	// this is so awful. i'm sure there's a better way, but i'm tired.
+	if botFacingDir == botFacingUp || botFacingDir == botFacingDown {
+		if u.ArrayContains(adj, u.Vec2i{X: pos.X - 1, Y: pos.Y}) {
+			if botFacingDir == botFacingUp {
+				turnDirection = dirLeft
+			} else if botFacingDir == botFacingDown {
+				turnDirection = dirRight
+			}
+		} else if u.ArrayContains(adj, u.Vec2i{X: pos.X + 1, Y: pos.Y}) {
+			if botFacingDir == botFacingUp {
+				turnDirection = dirRight
+			} else if botFacingDir == botFacingDown {
+				turnDirection = dirLeft
+			}
+		}
+	} else {
+		if u.ArrayContains(adj, u.Vec2i{X: pos.X, Y: pos.Y - 1}) {
+			if botFacingDir == botFacingLeft {
+				turnDirection = dirRight
+			} else if botFacingDir == botFacingRight {
+				turnDirection = dirLeft
+			}
+		} else if u.ArrayContains(adj, u.Vec2i{X: pos.X, Y: pos.Y + 1}) {
+			if botFacingDir == botFacingLeft {
+				turnDirection = dirLeft
+			} else if botFacingDir == botFacingRight {
+				turnDirection = dirRight
+			}
+		}
+	}
+
+	dirAscii := "L"
+	if turnDirection == dirRight {
+		dirAscii = "R"
+	}
+
+	return turnDirection, dirAscii
+}
+
+func buildInstructionString(instructions []string) string {
+	workingInstructions := make([]string, len(instructions))
+	copy(workingInstructions, instructions)
+
+	minimumRecurrence := 3
+	initialInstructionSubsetLen := 4
+
+	instructionStr := strings.Join(workingInstructions, ",")
+	progs := make([][]string, 3)
+	for i := range progs {
+		numFound := minimumRecurrence
+		subLen := initialInstructionSubsetLen
+		for numFound >= minimumRecurrence {
+			numFound = 1
+			instructionSubset := strings.Join(workingInstructions[0:subLen], ",")
+			if len(instructionSubset) > maxInstructionSetLength {
+				break
+			}
+			for x := len(instructionSubset); x <= len(instructionStr)-len(instructionSubset); x++ {
+				if instructionStr[x:x+len(instructionSubset)] == instructionSubset {
+					numFound++
+					x += len(instructionSubset)
+				}
+			}
+			if numFound >= minimumRecurrence {
+				subLen += 2
+			}
+		}
+		if numFound < minimumRecurrence {
+			subLen -= 2
+		}
+		progs[i] = make([]string, subLen)
+		copy(progs[i], workingInstructions[0:subLen])
+
+		instructionStr = strings.ReplaceAll(instructionStr, strings.Join(progs[i], ","), "")
+		instructionStr = strings.TrimPrefix(strings.ReplaceAll(instructionStr, ",,", ","), ",")
+
+		if len(instructionStr) == 0 {
+			workingInstructions = nil
+		} else {
+			workingInstructions = strings.Split(instructionStr, ",")
+		}
+	}
+
+	if workingInstructions != nil {
+		panic("failed to use up all instructions")
+	}
+
+	programStr := strings.Join(instructions, ",")
+	for i := range progs {
+		programStr = strings.ReplaceAll(programStr, strings.Join(progs[i], ","), fmt.Sprintf("%c", 'A'+i))
+	}
+
+	sb := strings.Builder{}
+	sb.WriteString(programStr)
+	sb.WriteRune('\n')
+
+	for i := range progs {
+		sb.WriteString(strings.Join(progs[i], ","))
+		sb.WriteRune('\n')
+	}
+
+	runDebug := 'n'
+	sb.WriteRune(runDebug)
+	sb.WriteRune('\n')
+
+	return sb.String()
+}
+
+func (grid day17Grid) solvePath(botLocation u.Vec2i, botFacingDir botFacing) string {
+	instructions := make([]string, 0)
+
+	pos := botLocation
+	endLocation := grid.findEndLocation(botLocation)
+	for {
+		if pos == endLocation {
+			break
+		}
+
+		turnDirection, dirAscii := grid.getTurnDirectionFromCorner(pos, botFacingDir)
+		if turnDirection == 0 {
+			panic("at an invalid location somehow")
+		}
+
+		instructions = append(instructions, dirAscii)
+
+		botFacingDir = botFacingDir.getNewFacingDir(turnDirection)
+		numMoved := 0
+		for {
+			cell, newY, newX := grid.getCellTypeInDirection(pos.Y, pos.X, botFacingDir)
+			if cell != cellTypeScaffold {
+				break
+			}
+			pos.X = newX
+			pos.Y = newY
+			numMoved++
+		}
+		instructions = append(instructions, fmt.Sprintf("%d", numMoved))
+	}
+
+	return buildInstructionString(instructions)
+}
+
+func (d *Day17) Part1() string {
+	grid := day17Grid{}
+	y := 0
+	var botLocation u.Vec2i
+	var botFacingDir botFacing
+
+	d.program.RunIn(func(inputStep int) int64 {
+		return 0
+	}, func(val int64, state u.IntcodeProgramState) {
+		rVal := rune(val)
+		y, botLocation, botFacingDir = grid.processGridUpdate(y, rVal, botLocation, botFacingDir)
+	})
+
+	alignmentParameterTotal := 0
+	grid.forEachCellOfType(cellTypeScaffold, func(y, x int) {
+		if numSurrounding := len(grid.getAdjacentScaffolds(y, x)); numSurrounding == 4 {
+			alignmentParameterTotal += y * x
+		}
+	})
+
+	// endLocation := grid.findEndLocation(botLocation)
+	// grid.Draw(botLocation, botFacingDir, endLocation)
+
+	return fmt.Sprintf("Alignment parameter sum: %s%d%s", u.TextBold, alignmentParameterTotal, u.TextReset)
+}
+
+func (d *Day17) Part2() string {
+	beforeGrid := day17Grid{}
+	var beforeBotLocation u.Vec2i
+	var beforeBotFacing botFacing
+
+	afterGrid := day17Grid{}
+	var afterBotLocation u.Vec2i
+	var afterBotFacing botFacing
+
+	d.program.Reset()
+	d.program.SetMemory(0, 2)
+
+	row := 0
+	var outputState int
+	var lastOutput int64
+	var instructionStr string
+	d.program.RunIn(func(inputStep int) int64 {
+		return int64(instructionStr[inputStep-1])
+	}, func(val int64, state u.IntcodeProgramState) {
+		rVal := rune(val)
+		if outputState == 0 {
+			row, beforeBotLocation, beforeBotFacing = beforeGrid.processGridUpdate(row, rVal, beforeBotLocation, beforeBotFacing)
+		} else if outputState == 2 {
+			row, afterBotLocation, afterBotFacing = afterGrid.processGridUpdate(row, rVal, afterBotLocation, afterBotFacing)
+		}
+
+		if rVal == '\n' && lastOutput == '\n' {
+			if outputState == 0 {
+				instructionStr = beforeGrid.solvePath(beforeBotLocation, beforeBotFacing)
+			}
+			outputState++
+			row = 0
+		}
+
+		lastOutput = val
+	})
+
+	// fmt.Println("initial grid:")
+	// beforeEndLocation := beforeGrid.findEndLocation(beforeBotLocation)
+	// beforeGrid.Draw(beforeBotLocation, beforeBotFacing, beforeEndLocation)
+
+	// fmt.Println("completed grid:")
+	// afterEndLocation := afterGrid.findEndLocation(afterBotLocation)
+	// afterGrid.Draw(afterBotLocation, afterBotFacing, afterEndLocation)
+
+	return fmt.Sprintf("Dust collected after traveling all paths: %s%d%s", u.TextBold, lastOutput, u.TextReset)
+}

days/18.go

@@ -0,0 +1,345 @@
+package days
+
+import (
+	"container/heap"
+	"fmt"
+	"math"
+	"strings"
+
+	"github.com/edwingeng/deque/v2"
+	u "parnic.com/aoc2019/utilities"
+)
+
+type day18Cell int
+type day18Vec u.Vec2[int]
+type day18Graph map[rune][]u.Pair[rune, int]
+
+const (
+	day18CellWall day18Cell = iota
+	day18CellOpen
+)
+
+var (
+	day18AdjacentOffsets = []day18Vec{
+		{X: -1, Y: 0},
+		{X: 1, Y: 0},
+		{X: 0, Y: -1},
+		{X: 0, Y: 1},
+	}
+)
+
+type Day18 struct {
+	entrance day18Vec
+	grid     [][]day18Cell
+	doors    map[day18Vec]int
+	keys     map[day18Vec]int
+}
+
+func (d *Day18) Parse() {
+	d.doors = make(map[day18Vec]int)
+	d.keys = make(map[day18Vec]int)
+
+	lines := u.GetStringLines("18p")
+	d.grid = make([][]day18Cell, len(lines))
+	for i, line := range lines {
+		d.grid[i] = make([]day18Cell, len(line))
+		for j, char := range line {
+			if char == '#' {
+				d.grid[i][j] = day18CellWall
+			} else if char == '.' {
+				d.grid[i][j] = day18CellOpen
+			} else if char == '@' {
+				d.grid[i][j] = day18CellOpen
+				d.entrance = day18Vec{X: j, Y: i}
+			} else if char >= 'A' && char <= 'Z' {
+				d.grid[i][j] = day18CellOpen
+				d.doors[day18Vec{X: j, Y: i}] = int(char - 'A')
+			} else if char >= 'a' && char <= 'z' {
+				d.grid[i][j] = day18CellOpen
+				d.keys[day18Vec{X: j, Y: i}] = int(char - 'a')
+			}
+		}
+	}
+}
+
+func (d Day18) Num() int {
+	return 18
+}
+
+func (d Day18) Draw(grid [][]day18Cell, keys, doors map[day18Vec]int, entrances ...day18Vec) {
+	for y := range grid {
+		for x := range grid[y] {
+			switch grid[y][x] {
+			case day18CellWall:
+				fmt.Print("█")
+			case day18CellOpen:
+				posVec := day18Vec{X: x, Y: y}
+				if _, exists := doors[posVec]; exists {
+					fmt.Printf("%c", rune(doors[posVec]+'A'))
+				} else if _, exists := keys[posVec]; exists {
+					fmt.Printf("%c", rune(keys[posVec]+'a'))
+				} else if u.ArrayContains(entrances, posVec) {
+					fmt.Print("@")
+				} else {
+					fmt.Print(".")
+				}
+			}
+		}
+		fmt.Println()
+	}
+}
+
+func (d Day18) findAdjacentCells(inPos day18Vec, keys, doors map[day18Vec]int, grid [][]day18Cell) []u.Pair[rune, int] {
+	found := make([]u.Pair[rune, int], 0)
+
+	getAdjacent := func(pos day18Vec) []day18Vec {
+		retAdjacent := make([]day18Vec, 0, len(day18AdjacentOffsets))
+		for _, off := range day18AdjacentOffsets {
+			offVec := day18Vec{X: pos.X + off.X, Y: pos.Y + off.Y}
+			if grid[offVec.Y][offVec.X] == day18CellWall {
+				continue
+			}
+			retAdjacent = append(retAdjacent, offVec)
+		}
+
+		return retAdjacent
+	}
+
+	queue := deque.NewDeque[u.Pair[int, day18Vec]]()
+	visited := make(map[day18Vec]bool)
+	for _, adjacent := range getAdjacent(inPos) {
+		queue.PushBack(u.Pair[int, day18Vec]{First: 1, Second: adjacent})
+	}
+
+	for !queue.IsEmpty() {
+		next := queue.PopFront()
+
+		if _, exists := visited[next.Second]; !exists {
+			visited[next.Second] = true
+
+			key, adjacentIsKey := keys[next.Second]
+			door, adjacentIsDoor := doors[next.Second]
+			if adjacentIsKey || adjacentIsDoor {
+				var rVal rune
+				if adjacentIsKey {
+					rVal = rune('a' + key)
+				} else if adjacentIsDoor {
+					rVal = rune('A' + door)
+				}
+
+				alreadyFound := false
+				for _, p := range found {
+					if p.First == rVal {
+						alreadyFound = true
+						break
+					}
+				}
+				if !alreadyFound {
+					found = append(found, u.Pair[rune, int]{First: rVal, Second: next.First})
+					continue
+				}
+			}
+
+			for _, neighbor := range getAdjacent(next.Second) {
+				if _, exists := visited[neighbor]; !exists {
+					queue.PushBack(u.Pair[int, day18Vec]{First: next.First + 1, Second: neighbor})
+				}
+			}
+		}
+	}
+
+	return found
+}
+
+type day18PriorityQueue struct {
+	distance int
+	neighbor rune
+}
+type PriorityQueueHeap []day18PriorityQueue
+
+func (h PriorityQueueHeap) Len() int           { return len(h) }
+func (h PriorityQueueHeap) Less(i, j int) bool { return h[i].distance < h[j].distance }
+func (h PriorityQueueHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
+
+func (h *PriorityQueueHeap) Push(x any) {
+	*h = append(*h, x.(day18PriorityQueue))
+}
+
+func (h *PriorityQueueHeap) Pop() any {
+	old := *h
+	n := len(old)
+	x := old[n-1]
+	*h = old[0 : n-1]
+	return x
+}
+
+type reachableKeysMemo struct {
+	pos       rune
+	keysFound int
+}
+
+var knownReachableKeys = make(map[reachableKeysMemo][]u.Pair[rune, int])
+
+func (d Day18) reachableKeys(inPos rune, keysFound int, graph day18Graph) []u.Pair[rune, int] {
+	memo := reachableKeysMemo{
+		pos:       inPos,
+		keysFound: keysFound,
+	}
+	if v, exists := knownReachableKeys[memo]; exists {
+		return v
+	}
+
+	ret := make([]u.Pair[rune, int], 0)
+	distance := make(map[rune]int)
+
+	ih := make(PriorityQueueHeap, 0)
+
+	for _, p := range graph[inPos] {
+		ih = append(ih, day18PriorityQueue{
+			distance: p.Second,
+			neighbor: p.First,
+		})
+	}
+
+	heap.Init(&ih)
+
+	for ih.Len() > 0 {
+		node := heap.Pop(&ih).(day18PriorityQueue)
+
+		// it's a key and we haven't picked it up yet...
+		if node.neighbor >= 'a' && node.neighbor <= 'z' && (1<<int(node.neighbor-'a')&keysFound) == 0 {
+			ret = append(ret, u.Pair[rune, int]{First: node.neighbor, Second: node.distance})
+			continue
+		}
+
+		// it's a door but we don't have the key yet...
+		if node.neighbor >= 'A' && node.neighbor <= 'Z' && ((1<<int(node.neighbor-'A'))&keysFound) == 0 {
+			continue
+		}
+
+		for _, p := range graph[node.neighbor] {
+			newDistance := node.distance + p.Second
+			if dist, exists := distance[p.First]; !exists || newDistance < dist {
+				distance[p.First] = newDistance
+				heap.Push(&ih, day18PriorityQueue{
+					distance: newDistance,
+					neighbor: p.First,
+				})
+			}
+		}
+	}
+
+	knownReachableKeys[memo] = ret
+	return ret
+}
+
+type minStepsMemo struct {
+	pos        string
+	keysToFind int
+	keysFound  int
+}
+
+var knownMinimumSteps = make(map[minStepsMemo]int, 0)
+
+func (d Day18) minimumSteps(inPos string, keysToFind int, keysFound int, graph day18Graph) int {
+	memo := minStepsMemo{
+		pos:        inPos,
+		keysToFind: keysToFind,
+		keysFound:  keysFound,
+	}
+	if v, exists := knownMinimumSteps[memo]; exists {
+		return v
+	}
+
+	if keysToFind == 0 {
+		return 0
+	}
+
+	best := math.Inf(1)
+	for _, item := range inPos {
+		for _, p := range d.reachableKeys(item, keysFound, graph) {
+			sb := strings.Builder{}
+			oldIdx := strings.IndexRune(inPos, item)
+			for i := range inPos {
+				if i == oldIdx {
+					sb.WriteRune(p.First)
+				} else {
+					sb.WriteByte(inPos[i])
+				}
+			}
+			newKeys := keysFound + (1 << (p.First - 'a'))
+			dist := p.Second
+
+			dist += d.minimumSteps(sb.String(), keysToFind-1, newKeys, graph)
+
+			if float64(dist) < best {
+				best = float64(dist)
+			}
+		}
+	}
+
+	knownMinimumSteps[memo] = int(best)
+	return int(best)
+}
+
+func (d Day18) buildGraph(pos []day18Vec, keys map[day18Vec]int, doors map[day18Vec]int, grid [][]day18Cell) day18Graph {
+	graph := make(day18Graph)
+	for i, p := range pos {
+		adjacent := d.findAdjacentCells(p, keys, doors, grid)
+		graph[rune('1'+i)] = adjacent
+	}
+	for keyPos, keyType := range keys {
+		graph[rune('a'+keyType)] = d.findAdjacentCells(keyPos, keys, doors, grid)
+	}
+	for doorPos, doorType := range doors {
+		graph[rune('A'+doorType)] = d.findAdjacentCells(doorPos, keys, doors, grid)
+	}
+
+	return graph
+}
+
+func (d Day18) part2PatchMap(grid [][]day18Cell, entrance day18Vec) []day18Vec {
+	grid[entrance.Y-1][entrance.X] = day18CellWall
+	grid[entrance.Y][entrance.X-1] = day18CellWall
+	grid[entrance.Y][entrance.X] = day18CellWall
+	grid[entrance.Y][entrance.X+1] = day18CellWall
+	grid[entrance.Y+1][entrance.X] = day18CellWall
+
+	return []day18Vec{
+		{X: entrance.X - 1, Y: entrance.Y - 1},
+		{X: entrance.X + 1, Y: entrance.Y - 1},
+		{X: entrance.X - 1, Y: entrance.Y + 1},
+		{X: entrance.X + 1, Y: entrance.Y + 1},
+	}
+}
+
+func (d *Day18) Part1() string {
+	// fmt.Println("initial state:")
+	// d.Draw(d.grid, d.keys, d.doors, d.entrance)
+
+	graph := d.buildGraph([]day18Vec{d.entrance}, d.keys, d.doors, d.grid)
+	minSteps := d.minimumSteps("1", len(d.keys), 0, graph)
+
+	return fmt.Sprintf("Total distance traveled: %s%d%s", u.TextBold, minSteps, u.TextReset)
+}
+
+func (d *Day18) Part2() string {
+	// fmt.Println("initial state:")
+	grid := make([][]day18Cell, len(d.grid))
+	for i := range d.grid {
+		grid[i] = make([]day18Cell, len(d.grid[i]))
+		copy(grid[i], d.grid[i])
+	}
+
+	entrances := d.part2PatchMap(grid, d.entrance)
+	// d.Draw(grid, d.keys, d.doors, entrances...)
+
+	// clear memoized maps that (might have) came from part1
+	knownMinimumSteps = make(map[minStepsMemo]int)
+	knownReachableKeys = make(map[reachableKeysMemo][]u.Pair[rune, int])
+
+	graph := d.buildGraph(entrances, d.keys, d.doors, grid)
+	minSteps := d.minimumSteps("1234", len(d.keys), 0, graph)
+
+	return fmt.Sprintf("Total distance traveled: %s%d%s", u.TextBold, minSteps, u.TextReset)
+}

go.mod

@@ -1,3 +1,5 @@
 module parnic.com/aoc2019
 
 go 1.18
+
+require github.com/edwingeng/deque/v2 v2.0.1

go.sum

@@ -0,0 +1,2 @@
+github.com/edwingeng/deque/v2 v2.0.1 h1:yNEsA9tUImO0vyw2hmVGiK4nnkoxBQ8stMYpdVq2ZmQ=
+github.com/edwingeng/deque/v2 v2.0.1/go.mod h1:HukI8CQe9KDmZCcURPZRYVYjH79Zy2tIjTF9sN3Bgb0=

inputs/17p.txt

@@ -0,0 +1 @@
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inputs/18p.txt

@@ -0,0 +1,81 @@
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inputs/18s1.txt

@@ -0,0 +1,3 @@
+#########
+#b.A.@.a#
+#########

inputs/18s2.txt

@@ -0,0 +1,5 @@
+########################
+#f.D.E.e.C.b.A.@.a.B.c.#
+######################.#
+#d.....................#
+########################

inputs/18s3.txt

@@ -0,0 +1,5 @@
+########################
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+#.######################
+#.....@.a.B.c.d.A.e.F.g#
+########################

inputs/18s4.txt

@@ -0,0 +1,9 @@
+#################
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+########.########
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+########@########
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+########.########
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+#################

inputs/18s5.txt

@@ -0,0 +1,6 @@
+########################
+#@..............ac.GI.b#
+###d#e#f################
+###A#B#C################
+###g#h#i################
+########################

inputs/18s6.txt

@@ -0,0 +1,7 @@
+#######
+#a.#Cd#
+##...##
+##.@.##
+##...##
+#cB#Ab#
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inputs/18s7.txt

@@ -0,0 +1,7 @@
+###############
+#d.ABC.#.....a#
+######...######
+######.@.######
+######...######
+#b.....#.....c#
+###############

inputs/18s8.txt

@@ -0,0 +1,7 @@
+#############
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+###C#...###J#
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inputs/18s9.txt

@@ -0,0 +1,9 @@
+#############
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+#nK.L...G...#
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+#o#m..#i#jk.#
+#############

main.go

@@ -47,6 +47,8 @@ var dayMap = []day{
 	&days.Day14{},
 	&days.Day15{},
 	&days.Day16{},
+	&days.Day17{},
+	&days.Day18{},
 }
 
 func main() {

utilities/map.go

@@ -15,3 +15,13 @@ func MapValues[T comparable, U any](m map[T]U) []U {
 	}
 	return r
 }
+
+// CopyMap returns a copy of the passed-in map. Note: currently only works if [U]
+// is not a map or slice.
+func CopyMap[T comparable, U any](m map[T]U) map[T]U {
+	r := make(map[T]U)
+	for k, v := range m {
+		r[k] = v
+	}
+	return r
+}

utilities/vector.go

@@ -13,6 +13,8 @@ type Vec3[T Number] struct {
 	Z T
 }
 
+type Vec2i Vec2[int]
+
 func (v Vec2[T]) Dot(other Vec2[T]) T {
 	return (v.X * other.X) + (v.Y * other.Y)
 }
@@ -42,11 +44,16 @@ func (v Vec2[T]) Equals(other Vec2[T]) bool {
 		v.Y == other.Y
 }
 
+func (v Vec2[T]) ManhattanDistance(other Vec2[T]) T {
+	return T(math.Abs(float64(v.X-other.X)) + math.Abs(float64(v.Y-other.Y)))
+}
+
 func VecBetween[T Number](a, b Vec2[T]) Vec2[T] {
-	return Vec2[T]{
-		X: a.X - b.X,
-		Y: a.Y - b.Y,
-	}
+	return a.To(b)
+}
+
+func ManhattanDistance[T Number](a, b Vec2[T]) T {
+	return a.ManhattanDistance(b)
 }
 
 func (v Vec3[T]) Dot(other Vec3[T]) T {