Day 15 solution

I wanted to use something like a right-hand wall solver, but the fact that you don't know the maze ahead of time and you can't see what something is without trying to move into it made that difficult. This semi-brute-force approach works well enough. I originally stopped as soon as I found the oxygen system and figured out the shortest path, but once I submitted that answer and saw that part 2 wanted the full map explored, I figured I might as well just fill the map all at once.

I think I would have been stuck on part 1 longer if my input set didn't happen to find the goal system fairly easily (or maybe my debug drawing helped me work through it with that input set specifically, I'm not sure) since a different input set required some tweaking to the max-visited threshold in order to find things that my first input set found with a lower setting.

Regardless, I'm pretty excited that I came to Trémaux's algorithm, more or less, on my own. I went to Wikipedia to see if I was on the right track and lo and behold, I had come to a version of it myself.

Part 2 turned out easier than I originally thought. I suspected this solution would work, but wasn't completely confident. It can only work for the type of maze used by this problem (where there are no loops of open areas). I'm just glad I didn't need A* or anything.

Oh, and this `stringer` command that allows debug printing of enums can be installed with `go install golang.org/x/tools/cmd/stringer@latest`

days/07.go

@@ -28,7 +28,7 @@ func (d *Day07) Part1() string {
 	var highestVal int64
 	var highestSequence []int64
 
-	allSequences := utilities.GetPermutations([]int64{0, 1, 2, 3, 4})
+	allSequences := utilities.GetPermutations([]int64{0, 1, 2, 3, 4}...)
 	for _, sequence := range allSequences {
 		if len(sequence) != len(d.amps) {
 			panic("input sequence does not match up to number of amplifiers")
@@ -68,7 +68,7 @@ func (d *Day07) Part2() string {
 	var highestVal int64
 	var highestSequence []int64
 
-	allSequences := utilities.GetPermutations([]int64{5, 6, 7, 8, 9})
+	allSequences := utilities.GetPermutations([]int64{5, 6, 7, 8, 9}...)
 	for _, sequence := range allSequences {
 		if len(sequence) != len(d.amps) {
 			panic("input sequence does not match up to number of amplifiers")

days/15.go

@@ -0,0 +1,332 @@
+package days
+
+//go:generate stringer -type=cellStatus,responseType,dirType -output=15_types_string.go
+
+import (
+	"fmt"
+	"math"
+	"sort"
+
+	u "parnic.com/aoc2019/utilities"
+)
+
+type point u.Pair[int, int]
+type cellStatus int
+type responseType int
+type dirType int
+
+const (
+	cellStatusUnknown cellStatus = iota
+	cellStatusWall
+	cellStatusOpen
+	cellStatusGoal
+)
+
+const (
+	responseWall responseType = iota
+	responseSuccess
+	responseFoundGoal
+)
+
+const maxVisited = 3
+
+const (
+	dirNorth dirType = iota + 1
+	dirSouth
+	dirWest
+	dirEast
+
+	dirFirst = dirNorth
+	dirLast  = dirEast
+)
+
+var dirOrders = [][]dirType{
+	{dirNorth, dirSouth, dirWest, dirEast},
+	{dirSouth, dirWest, dirEast, dirNorth},
+	{dirWest, dirEast, dirNorth, dirSouth},
+	{dirEast, dirNorth, dirSouth, dirWest},
+}
+
+// turned out to be unnecessary on multiple datasets i tried. increases the iterations 6x
+// var dirOrders = u.GetPermutations(dirNorth, dirSouth, dirWest, dirEast)
+
+type visitedStatus struct {
+	timesVisited      int
+	distanceFromStart int
+}
+
+type Day15 struct {
+	program      u.IntcodeProgram
+	grid         map[point]cellStatus
+	visited      map[point]*visitedStatus
+	shortestPath []point
+	pos          point
+	goalPos      point
+}
+
+func (d *Day15) Parse() {
+	d.program = u.LoadIntcodeProgram("15p")
+	d.grid = map[point]cellStatus{
+		{First: 0, Second: 0}: cellStatusOpen,
+	}
+	d.visited = map[point]*visitedStatus{
+		{First: 0, Second: 0}: {timesVisited: 1},
+	}
+	d.shortestPath = []point{{}}
+}
+
+func (d Day15) Num() int {
+	return 15
+}
+
+func (d Day15) getPointInDirection(pos point, dir dirType) point {
+	target := pos
+	switch dir {
+	case dirNorth:
+		target.First--
+	case dirSouth:
+		target.First++
+	case dirWest:
+		target.Second--
+	case dirEast:
+		target.Second++
+	}
+
+	return target
+}
+
+func (d Day15) getCellTypeInDirection(pos point, dir dirType) (cellStatus, point) {
+	target := d.getPointInDirection(pos, dir)
+	return d.grid[target], target
+}
+
+func (d Day15) getAdjacentCellsOfType(pos point, cellType cellStatus) []point {
+	points := make([]point, 0, 4)
+	for i := dirFirst; i <= dirLast; i++ {
+		adjacentCell := d.getPointInDirection(pos, i)
+		if d.grid[adjacentCell] == cellType {
+			points = append(points, adjacentCell)
+		}
+	}
+	return points
+}
+
+func (d Day15) getDirToNextCellType(pos point, t cellStatus, maxNumVisited int, dirs []dirType) (dirType, point, error) {
+	for _, dir := range dirs {
+		cellInDirection, targetCell := d.getCellTypeInDirection(pos, dir)
+		if cellInDirection == t {
+			_, visitedTargetExists := d.visited[targetCell]
+			foundUnknown := t == cellStatusUnknown && !visitedTargetExists
+			foundOther := t != cellStatusUnknown && visitedTargetExists && d.visited[targetCell].timesVisited <= maxNumVisited
+			if foundUnknown || foundOther {
+				return dir, targetCell, nil
+			}
+		}
+	}
+
+	return dirFirst, point{}, fmt.Errorf("no %v tiles around %v", t, pos)
+}
+
+func (d *Day15) Draw() {
+	min := point{First: math.MaxInt, Second: math.MaxInt}
+	max := point{First: math.MinInt, Second: math.MinInt}
+	for p := range d.grid {
+		if p.First < min.First {
+			min.First = p.First
+		}
+		if p.First > max.First {
+			max.First = p.First
+		}
+		if p.Second < min.Second {
+			min.Second = p.Second
+		}
+		if p.Second > max.Second {
+			max.Second = p.Second
+		}
+	}
+
+	for x := min.First; x <= max.First; x++ {
+		for y := min.Second; y <= max.Second; y++ {
+			p := point{First: x, Second: y}
+			switch d.grid[p] {
+			case cellStatusGoal:
+				fmt.Printf("%s@%s", u.ColorBrightGreen, u.TextReset)
+			case cellStatusOpen:
+				if p == d.pos {
+					fmt.Print(u.BackgroundBrightRed)
+				} else if x == 0 && y == 0 {
+					fmt.Print(u.BackgroundYellow)
+				} else if u.ArrayContains(d.shortestPath, p) {
+					fmt.Print(u.BackgroundGreen)
+				} else if d.visited[p] != nil && d.visited[p].timesVisited > maxVisited {
+					fmt.Print(u.ColorYellow)
+					fmt.Print(u.BackgroundBlack)
+				} else if d.visited[p] != nil && d.visited[p].timesVisited > 1 {
+					fmt.Print(u.BackgroundMagenta)
+				} else {
+					fmt.Print(u.BackgroundBlue)
+				}
+				fmt.Printf(".%s", u.TextReset)
+			case cellStatusWall:
+				fmt.Print("█")
+			case cellStatusUnknown:
+				fmt.Print(" ")
+			}
+		}
+		fmt.Println()
+	}
+}
+
+func (d *Day15) markShortestPath() {
+	pos := d.goalPos
+	checkOffsets := []point{
+		{First: -1, Second: 0},
+		{First: 1, Second: 0},
+		{First: 0, Second: -1},
+		{First: 0, Second: 1},
+	}
+
+	checkPt := func(pt point) (bool, int) {
+		if v, exists := d.visited[pt]; exists && d.grid[pt] == cellStatusOpen {
+			return true, v.distanceFromStart
+		}
+		return false, math.MaxInt
+	}
+
+	d.shortestPath = []point{d.goalPos}
+
+	for pos.First != 0 || pos.Second != 0 {
+		lowestDist := math.MaxInt
+		lowestPoint := point{}
+		for _, pt := range checkOffsets {
+			newPt := point{First: pos.First + pt.First, Second: pos.Second + pt.Second}
+			if found, dist := checkPt(newPt); found && dist < lowestDist {
+				lowestDist = dist
+				lowestPoint = newPt
+			}
+		}
+
+		d.shortestPath = append(d.shortestPath, lowestPoint)
+		pos = lowestPoint
+	}
+}
+
+func (d *Day15) exploreFullMap() map[point]*visitedStatus {
+	grids := make([]map[point]cellStatus, 0, len(dirOrders))
+	goalVisited := d.visited
+
+	for _, dirOrder := range dirOrders {
+		d.program.Reset()
+
+		targetPos := point{}
+		nextDir := dirFirst
+		distFromStart := 0
+
+		d.pos = point{}
+		d.visited = map[point]*visitedStatus{
+			{First: 0, Second: 0}: {timesVisited: 1},
+		}
+		d.grid = map[point]cellStatus{
+			{First: 0, Second: 0}: cellStatusOpen,
+		}
+		d.program.RunIn(func(inputStep int) int64 {
+			var err error
+			nextDir, targetPos, err = d.getDirToNextCellType(d.pos, cellStatusUnknown, 0, dirOrder)
+			if err != nil {
+				// ensure we never try to go back into the trapped spot
+				d.visited[d.pos].timesVisited = maxVisited + 1
+				for x := 1; x <= maxVisited && err != nil; x++ {
+					nextDir, targetPos, err = d.getDirToNextCellType(d.pos, cellStatusOpen, x, dirOrder)
+				}
+			}
+			if err != nil {
+				// d.Draw()
+				// panic(err)
+				d.program.Stop()
+			}
+
+			return int64(nextDir)
+		}, func(val int64, state u.IntcodeProgramState) {
+			rVal := responseType(val)
+
+			p := d.getPointInDirection(d.pos, nextDir)
+			shouldMove := true
+			switch rVal {
+			case responseWall:
+				d.grid[p] = cellStatusWall
+				shouldMove = false
+			case responseSuccess:
+				d.grid[p] = cellStatusOpen
+			case responseFoundGoal:
+				d.grid[p] = cellStatusGoal
+			}
+
+			if shouldMove {
+				d.pos = targetPos
+				if d.visited[d.pos] == nil {
+					d.visited[d.pos] = &visitedStatus{}
+					distFromStart++
+				} else {
+					distFromStart--
+				}
+				d.visited[d.pos].timesVisited++
+				d.visited[d.pos].distanceFromStart = distFromStart
+			}
+
+			if rVal == responseFoundGoal {
+				// d.Draw()
+				d.goalPos = targetPos
+				goalVisited = d.visited
+			}
+		})
+
+		grids = append(grids, d.grid)
+	}
+
+	d.grid = map[point]cellStatus{
+		{First: 0, Second: 0}: cellStatusOpen,
+	}
+	for _, grid := range grids {
+		keys := u.MapKeys(grid)
+		for _, key := range keys {
+			d.grid[key] = grid[key]
+		}
+	}
+
+	return goalVisited
+}
+
+func (d *Day15) tagDistanceRecursive(pos, last point, dist int, distances map[point]int) {
+	distances[pos] = dist
+	for _, cell := range d.getAdjacentCellsOfType(pos, cellStatusOpen) {
+		if cell == last {
+			continue
+		}
+		d.tagDistanceRecursive(cell, pos, dist+1, distances)
+	}
+}
+
+func (d *Day15) Part1() string {
+	d.visited = d.exploreFullMap()
+	d.markShortestPath()
+
+	for _, visited := range d.visited {
+		visited.timesVisited = 1
+	}
+	d.pos = point{}
+	// d.Draw()
+
+	return fmt.Sprintf("Moves required to reach target: %s%d%s", u.TextBold, d.visited[d.goalPos].distanceFromStart, u.TextReset)
+}
+
+func (d *Day15) Part2() string {
+	startLoc := d.goalPos
+	distanceMap := map[point]int{startLoc: 0}
+
+	d.tagDistanceRecursive(startLoc, point{}, 0, distanceMap)
+
+	cellDistances := u.MapValues(distanceMap)
+	sort.Slice(cellDistances, func(i, j int) bool { return cellDistances[i] > cellDistances[j] })
+
+	return fmt.Sprintf("Time to fill the area with oxygen: %s%d%s minutes", u.TextBold, cellDistances[0], u.TextReset)
+}

days/15_types_string.go

@@ -0,0 +1,66 @@
+// Code generated by "stringer -type=cellStatus,responseType,dirType -output=15_types_string.go"; DO NOT EDIT.
+
+package days
+
+import "strconv"
+
+func _() {
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	var x [1]struct{}
+	_ = x[cellStatusUnknown-0]
+	_ = x[cellStatusWall-1]
+	_ = x[cellStatusOpen-2]
+	_ = x[cellStatusGoal-3]
+}
+
+const _cellStatus_name = "cellStatusUnknowncellStatusWallcellStatusOpencellStatusGoal"
+
+var _cellStatus_index = [...]uint8{0, 17, 31, 45, 59}
+
+func (i cellStatus) String() string {
+	if i < 0 || i >= cellStatus(len(_cellStatus_index)-1) {
+		return "cellStatus(" + strconv.FormatInt(int64(i), 10) + ")"
+	}
+	return _cellStatus_name[_cellStatus_index[i]:_cellStatus_index[i+1]]
+}
+func _() {
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	var x [1]struct{}
+	_ = x[responseWall-0]
+	_ = x[responseSuccess-1]
+	_ = x[responseFoundGoal-2]
+}
+
+const _responseType_name = "responseWallresponseSuccessresponseFoundGoal"
+
+var _responseType_index = [...]uint8{0, 12, 27, 44}
+
+func (i responseType) String() string {
+	if i < 0 || i >= responseType(len(_responseType_index)-1) {
+		return "responseType(" + strconv.FormatInt(int64(i), 10) + ")"
+	}
+	return _responseType_name[_responseType_index[i]:_responseType_index[i+1]]
+}
+func _() {
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	var x [1]struct{}
+	_ = x[dirNorth-1]
+	_ = x[dirSouth-2]
+	_ = x[dirWest-3]
+	_ = x[dirEast-4]
+}
+
+const _dirType_name = "dirNorthdirSouthdirWestdirEast"
+
+var _dirType_index = [...]uint8{0, 8, 16, 23, 30}
+
+func (i dirType) String() string {
+	i -= 1
+	if i < 0 || i >= dirType(len(_dirType_index)-1) {
+		return "dirType(" + strconv.FormatInt(int64(i+1), 10) + ")"
+	}
+	return _dirType_name[_dirType_index[i]:_dirType_index[i+1]]
+}

inputs/15p.txt

@@ -0,0 +1 @@
+3,1033,1008,1033,1,1032,1005,1032,31,1008,1033,2,1032,1005,1032,58,1008,1033,3,1032,1005,1032,81,1008,1033,4,1032,1005,1032,104,99,102,1,1034,1039,101,0,1036,1041,1001,1035,-1,1040,1008,1038,0,1043,102,-1,1043,1032,1,1037,1032,1042,1105,1,124,102,1,1034,1039,1001,1036,0,1041,1001,1035,1,1040,1008,1038,0,1043,1,1037,1038,1042,1105,1,124,1001,1034,-1,1039,1008,1036,0,1041,1001,1035,0,1040,1001,1038,0,1043,1002,1037,1,1042,1105,1,124,1001,1034,1,1039,1008,1036,0,1041,102,1,1035,1040,101,0,1038,1043,1001,1037,0,1042,1006,1039,217,1006,1040,217,1008,1039,40,1032,1005,1032,217,1008,1040,40,1032,1005,1032,217,1008,1039,3,1032,1006,1032,165,1008,1040,33,1032,1006,1032,165,1101,0,2,1044,1105,1,224,2,1041,1043,1032,1006,1032,179,1101,1,0,1044,1106,0,224,1,1041,1043,1032,1006,1032,217,1,1042,1043,1032,1001,1032,-1,1032,1002,1032,39,1032,1,1032,1039,1032,101,-1,1032,1032,101,252,1032,211,1007,0,37,1044,1106,0,224,1102,1,0,1044,1105,1,224,1006,1044,247,101,0,1039,1034,101,0,1040,1035,1001,1041,0,1036,1002,1043,1,1038,101,0,1042,1037,4,1044,1106,0,0,42,4,15,10,25,91,86,34,69,14,50,9,24,24,54,10,18,63,17,2,88,36,31,60,20,13,20,76,94,25,41,36,78,3,39,17,94,10,25,22,16,67,72,31,47,15,25,66,8,17,54,8,89,67,29,28,92,11,54,14,4,64,78,28,80,66,6,70,36,56,13,63,17,19,83,17,27,29,34,54,4,93,24,71,6,66,22,21,92,93,39,4,31,76,72,25,74,89,18,62,18,27,57,35,83,39,14,23,95,2,79,25,97,86,13,79,1,34,90,81,29,45,31,38,67,17,92,32,31,50,1,42,81,1,2,87,7,52,74,20,85,22,32,47,16,77,96,28,14,74,22,55,15,75,44,29,19,8,73,2,54,18,26,64,95,21,98,48,25,36,11,78,77,5,16,70,18,10,76,51,51,10,25,43,56,12,13,48,8,17,68,10,64,25,93,42,3,52,24,72,99,23,54,13,44,17,15,8,68,59,15,95,61,9,50,8,51,23,8,39,13,95,64,12,28,56,90,1,62,27,12,60,6,5,18,24,13,99,12,18,92,97,7,56,22,48,91,34,87,32,98,20,89,74,16,51,84,21,46,14,23,52,17,57,12,50,17,97,23,99,11,21,68,21,61,89,13,45,64,89,18,36,40,35,90,9,1,3,81,33,32,83,99,97,34,4,46,31,21,90,62,14,93,11,22,99,51,70,88,51,2,4,29,36,35,48,17,25,30,69,34,3,39,89,31,89,33,30,88,77,18,30,67,17,40,61,19,40,85,26,23,49,22,41,30,13,79,6,34,40,33,43,49,84,19,78,43,10,74,18,61,15,22,51,86,2,78,11,33,92,24,88,27,24,44,2,97,4,4,49,72,93,24,65,79,21,60,33,46,36,22,15,87,33,78,2,49,70,7,78,78,11,14,64,41,61,41,6,1,49,35,78,47,65,14,66,10,86,76,2,32,88,3,24,14,87,9,95,32,19,4,10,67,60,15,19,53,47,24,29,65,5,95,35,1,70,16,43,53,11,64,17,34,84,74,65,30,18,58,2,35,48,38,33,46,16,87,27,12,79,11,88,35,7,5,35,67,83,38,6,17,56,82,13,45,32,30,67,25,62,7,43,63,9,36,14,58,53,25,98,12,38,78,13,63,93,33,11,54,9,66,32,79,62,47,28,6,67,31,53,71,2,30,59,12,90,59,67,2,58,52,1,30,51,49,22,89,88,27,19,41,27,13,19,76,5,82,58,12,49,51,17,15,73,35,25,74,90,29,14,96,83,69,11,18,14,10,40,93,35,31,35,36,58,36,16,48,7,66,98,31,47,34,47,33,5,28,82,88,1,30,80,95,32,87,2,19,91,74,74,19,8,25,63,65,51,30,14,41,98,99,21,90,15,91,3,31,74,27,31,77,28,74,4,27,88,82,11,54,35,52,13,88,71,93,20,82,18,36,68,33,83,1,18,5,42,46,29,62,10,78,67,9,84,48,22,33,74,36,53,58,31,5,8,55,10,24,49,34,81,1,4,86,5,25,2,75,36,49,2,24,88,72,8,64,36,38,10,23,36,93,28,51,90,4,99,57,31,10,14,94,21,27,61,34,70,41,32,14,91,20,83,30,54,26,44,30,85,96,87,35,16,61,99,16,32,53,68,87,1,89,43,9,17,4,39,50,61,8,49,27,48,13,51,34,47,30,89,68,50,18,63,99,50,32,41,33,71,1,43,57,64,24,95,9,89,8,64,18,75,23,97,74,67,24,55,1,87,97,44,0,0,21,21,1,10,1,0,0,0,0,0,0

main.go

@@ -45,6 +45,7 @@ var dayMap = []day{
 	&days.Day12{},
 	&days.Day13{},
 	&days.Day14{},
+	&days.Day15{},
 }
 
 func main() {

utilities/intcode.go

@@ -24,9 +24,10 @@ const (
 )
 
 type IntcodeProgram struct {
-	memory       []int64
+	memory        []int64
-	program      []int64
+	program       []int64
-	relativeBase int
+	relativeBase  int
+	haltRequested bool
 }
 
 type IntcodeProgramState struct {
@@ -147,7 +148,7 @@ func (p *IntcodeProgram) RunIn(inputFunc ProvideInputFunc, outputFunc ReceiveOut
 	p.init()
 
 	inputsRequested := 0
-	for instructionPointer := 0; instructionPointer < len(p.program); {
+	for instructionPointer := 0; instructionPointer < len(p.program) && !p.haltRequested; {
 		instruction := p.GetMemory(instructionPointer)
 		instructionPointer++
 
@@ -253,4 +254,10 @@ func (p *IntcodeProgram) RunIn(inputFunc ProvideInputFunc, outputFunc ReceiveOut
 			panic(fmt.Sprintf("exception executing program - unhandled opcode %d", opcode))
 		}
 	}
+
+	p.haltRequested = false
+}
+
+func (p *IntcodeProgram) Stop() {
+	p.haltRequested = true
 }

utilities/permutations.go

@@ -4,7 +4,7 @@ type Permutable interface {
 	~int | ~int8 | ~int16 | ~int32 | ~int64 | ~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64
 }
 
-func GetPermutations[T Permutable](arr []T) [][]T {
+func GetPermutations[T Permutable](arr ...T) [][]T {
 	var helper func([]T, int)
 	res := [][]T{}