Day 24 part 2

This isn't terribly slow (100ms right now) but I'd prefer it to be faster. I'm sure I could be smarter about which depths I'm scanning since a bunch of them can't possibly contain bugs, but whatever. This was about as rote and straightforward as I was expecting it to be, so at least there's that.

days/17.go

@@ -48,6 +48,7 @@ type Day17 struct {
 
 func (d *Day17) Parse() {
 	d.program = u.LoadIntcodeProgram("17p")
+	// d.program.SetDebugASCIIPrint(true)
 }
 
 func (d Day17) Num() int {
@@ -388,9 +389,8 @@ func (d *Day17) Part2() string {
 	row := 0
 	var outputState int
 	var lastOutput int64
-	var instructionStr string
 	d.program.RunIn(func(inputStep int) int64 {
-		return int64(instructionStr[inputStep-1])
+		panic("unexpected read")
 	}, func(val int64, state u.IntcodeProgramState) {
 		rVal := rune(val)
 		if outputState == 0 {
@@ -401,7 +401,7 @@ func (d *Day17) Part2() string {
 
 		if rVal == '\n' && lastOutput == '\n' {
 			if outputState == 0 {
-				instructionStr = beforeGrid.solvePath(beforeBotLocation, beforeBotFacing)
+				d.program.FeedInputString(beforeGrid.solvePath(beforeBotLocation, beforeBotFacing))
 			}
 			outputState++
 			row = 0

days/20.go

@@ -0,0 +1,398 @@
+package days
+
+import (
+	"container/heap"
+	"fmt"
+	"math"
+	"strings"
+
+	u "parnic.com/aoc2019/utilities"
+)
+
+type day20Cell int8
+type day20Graph map[day20Portal][]u.Pair[day20Portal, int]
+
+const (
+	day20CellWall day20Cell = iota
+	day20CellPath
+	day20CellDonutHole
+)
+
+var (
+	day20AdjacentOffsets = []u.Vec2i{
+		{X: -1, Y: 0},
+		{X: 1, Y: 0},
+		{X: 0, Y: -1},
+		{X: 0, Y: 1},
+	}
+
+	entrancePortal = day20Portal{name: "AA"}
+	exitPortal     = day20Portal{name: "ZZ"}
+)
+
+type day20Portal struct {
+	name  string
+	inner bool
+	depth int
+}
+
+type Day20 struct {
+	grid        [][]day20Cell
+	entrance    u.Vec2i
+	exit        u.Vec2i
+	portals     map[day20Portal]u.Vec2i
+	portalNames []string
+}
+
+func (d *Day20) Parse() {
+	d.portals = make(map[day20Portal]u.Vec2i)
+	d.portalNames = make([]string, 0)
+
+	lines := u.GetStringLines("20p")
+	d.grid = make([][]day20Cell, len(lines)-4)
+	currPortal := strings.Builder{}
+
+	for row, line := range lines {
+		y := row - 2
+		isGridRow := row >= 2 && row < len(lines)-2
+
+		if isGridRow {
+			d.grid[y] = make([]day20Cell, len(line)-4)
+		}
+
+		for col, ch := range lines[row] {
+			x := col - 2
+			isGridCol := col >= 2 && col < len(line)-2
+
+			if isGridRow && isGridCol {
+				if ch == '#' {
+					d.grid[y][x] = day20CellWall
+				} else if ch == '.' {
+					d.grid[y][x] = day20CellPath
+				} else {
+					d.grid[y][x] = day20CellDonutHole
+				}
+			}
+
+			if ch >= 'A' && ch <= 'Z' {
+				portalX := 0
+				portalY := 0
+				if len(line) > col+1 && line[col+1] >= 'A' && line[col+1] <= 'Z' {
+					currPortal.WriteRune(ch)
+					currPortal.WriteRune(rune(line[col+1]))
+
+					if len(line) > col+2 && line[col+2] == '.' {
+						portalY = y
+						portalX = x + 2
+					} else if col-1 >= 0 && line[col-1] == '.' {
+						portalY = y
+						portalX = x - 1
+					} else {
+						panic("!")
+					}
+				} else if len(lines) > row+1 && lines[row+1][col] >= 'A' && lines[row+1][col] <= 'Z' {
+					currPortal.WriteRune(ch)
+					currPortal.WriteRune(rune(lines[row+1][col]))
+
+					if len(lines) > row+2 && lines[row+2][col] == '.' {
+						portalY = y + 2
+						portalX = x
+					} else if row-1 >= 0 && lines[row-1][col] == '.' {
+						portalY = y - 1
+						portalX = x
+					} else {
+						panic("!")
+					}
+				}
+
+				if currPortal.Len() == 2 {
+					portalName := currPortal.String()
+					portalVec := u.Vec2i{X: portalX, Y: portalY}
+
+					if portalName == entrancePortal.name {
+						d.entrance = portalVec
+					} else if portalName == exitPortal.name {
+						d.exit = portalVec
+					} else {
+						portal := day20Portal{
+							name:  portalName,
+							inner: !d.isOuterPortal(portalVec),
+						}
+						d.portals[portal] = portalVec
+
+						u.AddToArray(&d.portalNames, portalName)
+					}
+
+					currPortal.Reset()
+				}
+			}
+		}
+	}
+}
+
+func (d Day20) Num() int {
+	return 20
+}
+
+func (d Day20) isPortal(vec u.Vec2i) (bool, int) {
+	if d.grid[vec.Y][vec.X] != day20CellPath {
+		return false, 0
+	}
+
+	for i, name := range d.portalNames {
+		p, exists := d.portals[day20Portal{name: name, inner: !d.isOuterPortal(vec)}]
+		if exists && vec == p {
+			return true, i
+		}
+	}
+
+	return false, 0
+}
+
+func (d Day20) Draw() {
+	for y := range d.grid {
+		for x := range d.grid[y] {
+			switch d.grid[y][x] {
+			case day20CellWall:
+				fmt.Print("█")
+			case day20CellDonutHole:
+				fmt.Print(" ")
+			case day20CellPath:
+				posVec := u.Vec2i{X: x, Y: y}
+				if posVec == d.entrance {
+					fmt.Print("@")
+				} else if posVec == d.exit {
+					fmt.Print("!")
+				} else {
+					isPortal, portalIdx := d.isPortal(posVec)
+					if isPortal {
+						ch := 'a' + portalIdx
+						if ch > 'z' {
+							ch = 'A' + (portalIdx - 26)
+						}
+						fmt.Printf("%c", ch)
+					} else {
+						fmt.Print(" ")
+					}
+				}
+			}
+		}
+
+		fmt.Println()
+	}
+}
+
+func (d Day20) isOuterPortal(pos u.Vec2i) bool {
+	return pos.X == 0 || pos.Y == 0 || pos.X == len(d.grid[0])-1 || pos.Y == len(d.grid)-1
+}
+
+func (d Day20) findAdjacentCells(inPos u.Vec2i) []u.Pair[day20Portal, int] {
+	found := make([]u.Pair[day20Portal, int], 0)
+
+	getAdjacent := func(pos u.Vec2i) []u.Vec2i {
+		retAdjacent := make([]u.Vec2i, 0, len(day20AdjacentOffsets))
+		for _, off := range day20AdjacentOffsets {
+			offVec := u.Vec2i{X: pos.X + off.X, Y: pos.Y + off.Y}
+			if offVec.Y < 0 || offVec.Y >= len(d.grid) || offVec.X < 0 || offVec.X >= len(d.grid[0]) {
+				continue
+			}
+			if d.grid[offVec.Y][offVec.X] != day20CellPath {
+				continue
+			}
+			retAdjacent = append(retAdjacent, offVec)
+		}
+
+		return retAdjacent
+	}
+
+	queue := make([]u.Pair[int, u.Vec2i], 0)
+	visited := map[u.Vec2i]bool{
+		inPos: true,
+	}
+	for _, adjacent := range getAdjacent(inPos) {
+		queue = append(queue, u.Pair[int, u.Vec2i]{First: 1, Second: adjacent})
+	}
+
+	for len(queue) > 0 {
+		next := queue[0]
+		queue = queue[1:]
+
+		if _, exists := visited[next.Second]; !exists {
+			visited[next.Second] = true
+
+			adjacentIsPortal, portalIdx := d.isPortal(next.Second)
+			if adjacentIsPortal || next.Second == d.entrance || next.Second == d.exit {
+				var portalName string
+				if next.Second == d.entrance {
+					portalName = entrancePortal.name
+				} else if next.Second == d.exit {
+					portalName = exitPortal.name
+				} else {
+					portalName = d.portalNames[portalIdx]
+				}
+
+				alreadyFound := false
+				for _, p := range found {
+					if p.First.name == portalName {
+						alreadyFound = true
+						break
+					}
+				}
+				if !alreadyFound {
+					found = append(found, u.Pair[day20Portal, int]{First: day20Portal{
+						name:  portalName,
+						inner: !d.isOuterPortal(next.Second),
+					}, Second: next.First})
+					continue
+				}
+			}
+
+			for _, neighbor := range getAdjacent(next.Second) {
+				if _, exists := visited[neighbor]; !exists {
+					queue = append(queue, u.Pair[int, u.Vec2i]{First: next.First + 1, Second: neighbor})
+				}
+			}
+		}
+	}
+
+	return found
+}
+
+type day20PriorityQueue struct {
+	distance int
+	neighbor day20Portal
+}
+type day20PriorityQueueHeap []day20PriorityQueue
+
+func (h day20PriorityQueueHeap) Len() int           { return len(h) }
+func (h day20PriorityQueueHeap) Less(i, j int) bool { return h[i].distance < h[j].distance }
+func (h day20PriorityQueueHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
+
+func (h *day20PriorityQueueHeap) Push(x any) {
+	*h = append(*h, x.(day20PriorityQueue))
+}
+
+func (h *day20PriorityQueueHeap) Pop() any {
+	old := *h
+	n := len(old)
+	x := old[n-1]
+	*h = old[0 : n-1]
+	return x
+}
+
+func (d Day20) dijkstra(graph day20Graph, start, end day20Portal, neighborFunc func(inPortal day20Portal) []u.Pair[day20Portal, int]) int {
+	distance := make(map[day20Portal]int)
+
+	ih := day20PriorityQueueHeap{
+		day20PriorityQueue{
+			distance: 0,
+			neighbor: start,
+		},
+	}
+
+	heap.Init(&ih)
+	visited := make(map[day20Portal]bool)
+
+	for ih.Len() > 0 {
+		node := heap.Pop(&ih).(day20PriorityQueue)
+
+		if node.neighbor == end {
+			return node.distance
+		}
+
+		if _, exists := visited[node.neighbor]; exists {
+			continue
+		}
+
+		visited[node.neighbor] = true
+
+		for _, p := range neighborFunc(node.neighbor) {
+			if _, exists := visited[p.First]; exists {
+				continue
+			}
+
+			newDistance := node.distance + p.Second
+			if dist, exists := distance[p.First]; !exists || newDistance < dist {
+				distance[p.First] = newDistance
+				heap.Push(&ih, day20PriorityQueue{
+					distance: newDistance,
+					neighbor: p.First,
+				})
+			}
+		}
+	}
+
+	return math.MaxInt
+}
+
+func (d Day20) buildGraph() day20Graph {
+	graph := make(day20Graph, len(d.portals)+1)
+
+	adjacent := d.findAdjacentCells(d.entrance)
+	graph[entrancePortal] = adjacent
+
+	for portal, portalVec := range d.portals {
+		adjacent = d.findAdjacentCells(portalVec)
+		graph[portal] = adjacent
+	}
+
+	return graph
+}
+
+func (d Day20) getDepthNeighbors(graph day20Graph, portal day20Portal) []u.Pair[day20Portal, int] {
+	basePortal := portal
+	basePortal.depth = 0
+	baseNeighbors := graph[basePortal]
+
+	neighbors := make([]u.Pair[day20Portal, int], 0)
+
+	if portal.inner {
+		n := day20Portal{name: portal.name, inner: false, depth: portal.depth + 1}
+		neighbors = append(neighbors, u.Pair[day20Portal, int]{First: n, Second: 1})
+	}
+
+	if portal.depth == 0 {
+		for _, i := range baseNeighbors {
+			if i.First.inner || i.First.name == entrancePortal.name || i.First.name == exitPortal.name {
+				neighbors = append(neighbors, u.Pair[day20Portal, int]{First: i.First, Second: i.Second})
+			}
+		}
+	} else {
+		if !portal.inner {
+			n := day20Portal{name: portal.name, inner: true, depth: portal.depth - 1}
+			neighbors = append(neighbors, u.Pair[day20Portal, int]{First: n, Second: 1})
+		}
+
+		for _, i := range baseNeighbors {
+			if i.First.name != entrancePortal.name && i.First.name != exitPortal.name {
+				n := day20Portal{name: i.First.name, inner: i.First.inner, depth: portal.depth}
+				neighbors = append(neighbors, u.Pair[day20Portal, int]{First: n, Second: i.Second})
+			}
+		}
+	}
+
+	return neighbors
+}
+
+func (d *Day20) Part1() string {
+	// d.Draw()
+
+	graph := d.buildGraph()
+
+	for portal, adjacent := range graph {
+		if portal.name == entrancePortal.name {
+			continue
+		}
+
+		graph[portal] = append(adjacent, u.Pair[day20Portal, int]{First: day20Portal{name: portal.name, inner: !portal.inner}, Second: 1})
+	}
+
+	distance := d.dijkstra(graph, entrancePortal, exitPortal, func(inPortal day20Portal) []u.Pair[day20Portal, int] { return graph[inPortal] })
+	return fmt.Sprintf("Steps to traverse maze: %s%d%s", u.TextBold, distance, u.TextReset)
+}
+
+func (d *Day20) Part2() string {
+	graph := d.buildGraph()
+	distance := d.dijkstra(graph, entrancePortal, exitPortal, func(inPortal day20Portal) []u.Pair[day20Portal, int] { return d.getDepthNeighbors(graph, inPortal) })
+	return fmt.Sprintf("Steps to traverse recursive maze: %s%d%s", u.TextBold, distance, u.TextReset)
+}

days/21.go

@@ -0,0 +1,85 @@
+package days
+
+import (
+	"fmt"
+	"strings"
+
+	u "parnic.com/aoc2019/utilities"
+)
+
+type Day21 struct {
+	program u.IntcodeProgram
+}
+
+func (d *Day21) Parse() {
+	d.program = u.LoadIntcodeProgram("21p")
+	// d.program.SetDebugASCIIPrint(true)
+}
+
+func (d Day21) Num() int {
+	return 21
+}
+
+func (d *Day21) Part1() string {
+	// if there's any hole up to 3 ahead of us but there's ground where we'd land if we jumped
+	// (a jump takes 4 spaces), go ahead and jump
+	cmds := []string{
+		// check if a hole at 1 or 2 ahead
+		"NOT A T",
+		"NOT B J",
+		// store that result in J
+		"OR T J",
+		// check if a hole at 3 ahead
+		"NOT C T",
+		// store hole in 1, 2, or 3 in T
+		"OR J T",
+		// set J true if hole in 1, 2, or 3
+		"OR T J",
+		// set J true if also no hole at 4 ahead
+		"AND D J",
+		"WALK",
+	}
+	instructionStr := strings.Join(cmds, "\n") + "\n"
+	d.program.FeedInputString(instructionStr)
+
+	res := d.program.Run()
+
+	return fmt.Sprintf("Hull damage value when walking: %s%d%s", u.TextBold, res, u.TextReset)
+}
+
+func (d *Day21) Part2() string {
+	//   @
+	// #####.#.##.##.###
+	//    ABCDEFGHI
+	// using the first program, this kills us. if we jump, we land at D and H becomes our new D, so it won't jump again.
+	// but if we waited to jump until we got one more ahead, we'd be ok.
+	// so now we want to know essentially the same thing as part 1, but also if our multiple (immediate second jump) would be successful.
+	// in problem terms, that's: if there's a hole at 1 or 2 ahead, and there's a hole at C with ground at H, and there's ground at D.
+	// so now for the above example we'd wait to jump until here:
+	//     @
+	// #####.#.##.##.###
+	//      ABCDEFGHI
+	// and all will be well.
+	cmds := []string{
+		// check if a hole at 1 or 2 ahead
+		"NOT A J",
+		"NOT B T",
+		// store that result in J
+		"OR T J",
+		// check if a hole at 3 ahead...
+		"NOT C T",
+		// and ground at 8 ahead (so we can immediately jump again if needed)...
+		"AND H T",
+		// combine those into J
+		"OR T J",
+		// and ensure we also still have a place to land if we jumped right away
+		"AND D J",
+		"RUN",
+	}
+	instructionStr := strings.Join(cmds, "\n") + "\n"
+	d.program.FeedInputString(instructionStr)
+
+	res := d.program.Run()
+
+	return fmt.Sprintf("Hull damage value when running: %s%d%s", u.TextBold, res, u.TextReset)
+}

days/22.go

@@ -0,0 +1,155 @@
+package days
+
+import (
+	"fmt"
+	"math"
+	"math/big"
+	"strconv"
+	"strings"
+
+	u "parnic.com/aoc2019/utilities"
+)
+
+type day22Instruction int
+
+const (
+	day22InstructionNewStack day22Instruction = iota
+	day22InstructionCut
+	day22InstructionDealIncrement
+)
+
+type day22Shuffle struct {
+	instruction day22Instruction
+	arg         int
+}
+
+type Day22 struct {
+	shuffles []day22Shuffle
+}
+
+func (d *Day22) Parse() {
+	lines := u.GetStringLines("22p")
+	d.shuffles = make([]day22Shuffle, len(lines))
+
+	for idx, line := range lines {
+		split := strings.Split(line, " ")
+		if split[0] == "deal" {
+			if split[1] == "into" {
+				d.shuffles[idx] = day22Shuffle{instruction: day22InstructionNewStack}
+			} else if split[1] == "with" {
+				arg, err := strconv.Atoi(split[3])
+				if err != nil {
+					panic(err)
+				}
+				d.shuffles[idx] = day22Shuffle{
+					instruction: day22InstructionDealIncrement,
+					arg:         arg,
+				}
+			}
+		} else if split[0] == "cut" {
+			arg, err := strconv.Atoi(split[1])
+			if err != nil {
+				panic(err)
+			}
+			d.shuffles[idx] = day22Shuffle{
+				instruction: day22InstructionCut,
+				arg:         arg,
+			}
+		}
+	}
+}
+
+func (d Day22) Num() int {
+	return 22
+}
+
+func (d Day22) applyShuffle(s day22Shuffle, stack, scratch []int) {
+	switch s.instruction {
+	case day22InstructionNewStack:
+		for i := 0; i < len(stack)/2; i++ {
+			stack[i], stack[len(stack)-1-i] = stack[len(stack)-1-i], stack[i]
+		}
+
+		// there's probably a way to do these two in place...
+	case day22InstructionCut:
+		absArg := int(math.Abs(float64(s.arg)))
+		for i, v := range stack {
+			if s.arg > 0 {
+				if i < absArg {
+					scratch[len(scratch)-absArg+i] = v
+				} else {
+					scratch[i-absArg] = v
+				}
+			} else {
+				if i < absArg {
+					scratch[i] = stack[len(stack)-absArg+i]
+				} else {
+					scratch[i] = stack[i-absArg]
+				}
+			}
+		}
+		copy(stack, scratch)
+
+	case day22InstructionDealIncrement:
+		for i, v := range stack {
+			scratch[(i*s.arg)%len(stack)] = v
+		}
+		copy(stack, scratch)
+	}
+}
+
+func (d *Day22) Part1() string {
+	deckSize := 10007
+	// deckSize := 10
+
+	stack := make([]int, deckSize)
+	for i := range stack {
+		stack[i] = i
+	}
+
+	scratch := make([]int, len(stack))
+
+	for _, s := range d.shuffles {
+		d.applyShuffle(s, stack, scratch)
+	}
+
+	pos := -1
+	for i, v := range stack {
+		if v == 2019 {
+			pos = i
+			break
+		}
+	}
+
+	return fmt.Sprintf("Card 2019 is at position %s%d%s", u.TextBold, pos, u.TextReset)
+}
+
+func (d *Day22) Part2() string {
+	n, iter := big.NewInt(119315717514047), big.NewInt(101741582076661)
+	offset, increment := big.NewInt(0), big.NewInt(1)
+	for _, s := range d.shuffles {
+		switch s.instruction {
+		case day22InstructionNewStack:
+			increment.Mul(increment, big.NewInt(-1))
+			offset.Add(offset, increment)
+		case day22InstructionCut:
+			offset.Add(offset, big.NewInt(0).Mul(big.NewInt(int64(s.arg)), increment))
+		case day22InstructionDealIncrement:
+			increment.Mul(increment, big.NewInt(0).Exp(big.NewInt(int64(s.arg)), big.NewInt(0).Sub(n, big.NewInt(2)), n))
+		}
+	}
+
+	finalIncr := big.NewInt(0).Exp(increment, iter, n)
+
+	finalOffs := big.NewInt(0).Exp(increment, iter, n)
+	finalOffs.Sub(big.NewInt(1), finalOffs)
+	invmod := big.NewInt(0).Exp(big.NewInt(0).Sub(big.NewInt(1), increment), big.NewInt(0).Sub(n, big.NewInt(2)), n)
+	finalOffs.Mul(finalOffs, invmod)
+	finalOffs.Mul(finalOffs, offset)
+
+	answer := big.NewInt(0).Mul(big.NewInt(2020), finalIncr)
+	answer.Add(answer, finalOffs)
+	answer.Mod(answer, n)
+
+	return fmt.Sprintf("Card at position 2020: %s%d%s", u.TextBold, answer, u.TextReset)
+}

days/23.go

@@ -0,0 +1,170 @@
+package days
+
+import (
+	"fmt"
+	"sync"
+
+	u "parnic.com/aoc2019/utilities"
+)
+
+type day23Computer struct {
+	program            u.IntcodeProgram
+	id                 int
+	packetQueue        chan u.Vec2[int64]
+	outputStep         int
+	nextPacketDest     int
+	sendingPacket      u.Vec2[int64]
+	hasQueuedPacket    bool
+	lastReceivedPacket u.Vec2[int64]
+	idle               bool
+}
+
+func (d Day23) makeComputer(id int) *day23Computer {
+	c := &day23Computer{
+		program:     d.program.Copy(),
+		id:          id,
+		packetQueue: make(chan u.Vec2[int64]),
+		idle:        true,
+	}
+
+	return c
+}
+
+type Day23 struct {
+	program u.IntcodeProgram
+}
+
+func (d *Day23) Parse() {
+	d.program = u.LoadIntcodeProgram("23p")
+}
+
+func (d Day23) Num() int {
+	return 23
+}
+
+func (d Day23) initComputers() []*day23Computer {
+	computers := make([]*day23Computer, 50)
+	for i := range computers {
+		computers[i] = d.makeComputer(i)
+	}
+	return computers
+}
+
+func (d Day23) execComputers(computers []*day23Computer, nat chan u.Vec2[int64]) *sync.WaitGroup {
+	wg := &sync.WaitGroup{}
+	wg.Add(len(computers))
+	for _, c := range computers {
+		go func(c *day23Computer) {
+			bootedUp := false
+			c.program.RunIn(func(inputStep int) int64 {
+				if !bootedUp {
+					bootedUp = true
+					return int64(c.id)
+				}
+
+				if c.hasQueuedPacket {
+					// fmt.Printf("  %d finished processing packet %v\n", c.id, c.lastReceivedPacket)
+					c.hasQueuedPacket = false
+					return c.lastReceivedPacket.Y
+				}
+
+				select {
+				case c.lastReceivedPacket = <-c.packetQueue:
+					// fmt.Printf("computer %d received packet %v\n", c.id, packet)
+					c.hasQueuedPacket = true
+					return c.lastReceivedPacket.X
+				default:
+					c.idle = true
+					return -1
+				}
+			}, func(val int64, state u.IntcodeProgramState) {
+				c.idle = false
+				switch c.outputStep {
+				case 0:
+					c.nextPacketDest = int(val)
+				case 1:
+					c.sendingPacket.X = val
+				case 2:
+					c.sendingPacket.Y = val
+
+					if c.nextPacketDest == 255 {
+						// fmt.Printf("computer %d sending %v to 255\n", c.id, c.sendingPacket)
+						nat <- c.sendingPacket
+					} else {
+						// fmt.Printf("computer %d sending %v to computer %d\n", c.id, c.sendingPacket, c.nextPacketDest)
+						computers[c.nextPacketDest].packetQueue <- c.sendingPacket
+					}
+				}
+
+				c.outputStep = (c.outputStep + 1) % 3
+			})
+
+			wg.Done()
+		}(c)
+	}
+
+	return wg
+}
+
+func (d *Day23) Part1() string {
+	computers := d.initComputers()
+	natChan := make(chan u.Vec2[int64])
+	wg := d.execComputers(computers, natChan)
+
+	answer := <-natChan
+	for _, c := range computers {
+		c.program.Stop()
+	}
+	// not really necessary, but let's make sure they all shut down in case
+	// we're running all days at once
+	wg.Wait()
+
+	return fmt.Sprintf("First packet sent to 255 Y value: %s%d%s", u.TextBold, answer.Y, u.TextReset)
+}
+
+func (d *Day23) Part2() string {
+	computers := d.initComputers()
+	natChan := make(chan u.Vec2[int64])
+	wg := d.execComputers(computers, natChan)
+
+	answerChan := make(chan int64)
+
+	go func() {
+		var currVal u.Vec2[int64]
+		var lastVal u.Vec2[int64]
+		hasReceived := false
+		for {
+			select {
+			case currVal = <-natChan:
+				hasReceived = true
+			default:
+			}
+
+			allIdle := true
+			for _, c := range computers {
+				if !c.idle {
+					allIdle = false
+					break
+				}
+			}
+
+			if allIdle && hasReceived {
+				// fmt.Printf("all idle, sending %v to computer 0\n", currVal)
+				if lastVal.Y == currVal.Y {
+					// fmt.Printf("found answer? %d\n", currVal.Y)
+					answerChan <- currVal.Y
+				}
+				computers[0].packetQueue <- currVal
+				lastVal = currVal
+			}
+		}
+	}()
+
+	answer := <-answerChan
+	for _, c := range computers {
+		c.program.Stop()
+	}
+	wg.Wait()
+
+	return fmt.Sprintf("First Y value sent to the NAT twice in a row: %s%d%s", u.TextBold, answer, u.TextReset)
+}

days/24.go

@@ -0,0 +1,289 @@
+package days
+
+import (
+	"fmt"
+	"math"
+
+	u "parnic.com/aoc2019/utilities"
+)
+
+var (
+	day24AdjacentOffsets = []u.Vec2i{
+		{X: -1, Y: 0},
+		{X: 1, Y: 0},
+		{X: 0, Y: -1},
+		{X: 0, Y: 1},
+	}
+)
+
+type Day24 struct {
+	grid [][]bool
+}
+
+func (d *Day24) Parse() {
+	lines := u.GetStringLines("24p")
+	d.grid = make([][]bool, len(lines))
+	for i, line := range lines {
+		d.grid[i] = make([]bool, len(line))
+		for j, ch := range line {
+			d.grid[i][j] = ch == '#'
+		}
+	}
+}
+
+func (d Day24) Num() int {
+	return 24
+}
+
+func (d Day24) calcActivatedNeighbors(grid [][]bool, i, j int) int {
+	activatedNeighbors := 0
+	for _, o := range day24AdjacentOffsets {
+		newI := i + o.X
+		newJ := j + o.Y
+		if newI < 0 || newI >= len(grid) || newJ < 0 || newJ >= len(grid[i]) {
+			continue
+		}
+		if grid[newI][newJ] {
+			activatedNeighbors++
+		}
+	}
+
+	return activatedNeighbors
+}
+
+func (d Day24) recursiveCalcActivatedNeighbors(gridMap map[int][][]bool, mapIdx, i, j int) int {
+	activatedNeighbors := 0
+	numNeighbors := 0
+	thisGrid := gridMap[mapIdx]
+	for _, o := range day24AdjacentOffsets {
+		newI := i + o.X
+		newJ := j + o.Y
+		if newI < 0 || newI >= len(thisGrid) || newJ < 0 || newJ >= len(thisGrid[i]) {
+			continue
+		}
+		if newI == 2 && newJ == 2 {
+			continue
+		}
+		numNeighbors++
+		if thisGrid[newI][newJ] {
+			activatedNeighbors++
+		}
+	}
+
+	checkLower := (i == 1 && j == 2) ||
+		(i == 2 && (j == 1 || j == 3)) ||
+		(i == 3 && j == 2)
+	if checkLower {
+		if lowerGrid, exists := gridMap[mapIdx+1]; exists {
+			if i == 1 {
+				for _, b := range lowerGrid[0] {
+					numNeighbors++
+					if b {
+						activatedNeighbors++
+					}
+				}
+			} else if i == 2 {
+				if j == 1 {
+					for _, r := range lowerGrid {
+						numNeighbors++
+						if r[0] {
+							activatedNeighbors++
+						}
+					}
+				} else if j == 3 {
+					for _, r := range lowerGrid {
+						numNeighbors++
+						if r[len(lowerGrid[0])-1] {
+							activatedNeighbors++
+						}
+					}
+				}
+			} else if i == 3 {
+				for _, b := range lowerGrid[len(lowerGrid)-1] {
+					numNeighbors++
+					if b {
+						activatedNeighbors++
+					}
+				}
+			}
+		}
+	}
+
+	checkUpper := (i == 0) || (i == len(thisGrid)-1) ||
+		((i != 0 && i != len(thisGrid)) && (j == 0 || j == len(thisGrid[0])-1))
+	if checkUpper {
+		if upperGrid, exists := gridMap[mapIdx-1]; exists {
+			if i == 0 {
+				numNeighbors++
+				if upperGrid[1][2] {
+					activatedNeighbors++
+				}
+			} else if i == len(thisGrid)-1 {
+				numNeighbors++
+				if upperGrid[3][2] {
+					activatedNeighbors++
+				}
+			}
+			if j == 0 {
+				numNeighbors++
+				if upperGrid[2][1] {
+					activatedNeighbors++
+				}
+			} else if j == len(thisGrid[0])-1 {
+				numNeighbors++
+				if upperGrid[2][3] {
+					activatedNeighbors++
+				}
+			}
+		}
+	}
+
+	return activatedNeighbors
+}
+
+func (d Day24) calcRating(grid [][]bool) int {
+	rating := 0
+	for i, r := range grid {
+		for j := range r {
+			pow := (i * len(r)) + j
+			if grid[i][j] {
+				result := int(math.Pow(2, float64(pow)))
+				rating += result
+			}
+		}
+	}
+	return rating
+}
+
+func (d Day24) numBugs(gridMap map[int][][]bool) int {
+	ret := 0
+	for _, v := range gridMap {
+		for _, r := range v {
+			for _, b := range r {
+				if b {
+					ret++
+				}
+			}
+		}
+	}
+	return ret
+}
+
+func copy2d[T comparable](dest [][]T, src [][]T) {
+	for i, r := range src {
+		copy(dest[i], r)
+	}
+}
+
+func (d Day24) Draw(grid [][]bool) {
+	for _, r := range grid {
+		for _, c := range r {
+			if c {
+				fmt.Print("#")
+			} else {
+				fmt.Print(".")
+			}
+		}
+		fmt.Println()
+	}
+	fmt.Println()
+}
+
+func (d *Day24) Part1() string {
+	grid := make([][]bool, len(d.grid))
+	scratch := make([][]bool, len(grid))
+	for i, g := range d.grid {
+		grid[i] = make([]bool, len(g))
+		scratch[i] = make([]bool, len(g))
+		copy(grid[i], d.grid[i])
+	}
+
+	found := false
+	answer := 0
+	seenRatings := make([]int, 0)
+	for i := 1; !found; i++ {
+		// d.Draw(grid)
+		for i, r := range grid {
+			for j := range r {
+				numActivated := d.calcActivatedNeighbors(grid, i, j)
+				if grid[i][j] {
+					scratch[i][j] = numActivated == 1
+				} else {
+					scratch[i][j] = numActivated == 1 || numActivated == 2
+				}
+			}
+		}
+
+		rating := d.calcRating(scratch)
+		if u.ArrayContains(seenRatings, rating) {
+			found = true
+			// d.Draw(scratch)
+			answer = rating
+		}
+		seenRatings = append(seenRatings, rating)
+		copy2d(grid, scratch)
+	}
+
+	return fmt.Sprintf("First repeated biodiversity rating is %s%d%s", u.TextBold, answer, u.TextReset)
+}
+
+func (d *Day24) Part2() string {
+	makeGrid := func(initialGrid [][]bool) ([][]bool, [][]bool) {
+		grid := make([][]bool, len(d.grid))
+		scratch := make([][]bool, len(grid))
+		for i, g := range d.grid {
+			grid[i] = make([]bool, len(g))
+			scratch[i] = make([]bool, len(g))
+			if initialGrid != nil {
+				copy(grid[i], initialGrid[i])
+			}
+		}
+
+		return grid, scratch
+	}
+
+	gridMap := make(map[int][][]bool)
+	scratchMap := make(map[int][][]bool)
+	gridMap[0], scratchMap[0] = makeGrid(d.grid)
+
+	min := 0
+	max := 0
+
+	for i := 0; i < 200; i++ {
+		gridMap[min-1], scratchMap[min-1] = makeGrid(nil)
+		gridMap[max+1], scratchMap[max+1] = makeGrid(nil)
+		min, max = min-1, max+1
+
+		// if i == 10 {
+		// 	keys := u.MapKeys(gridMap)
+		// 	sort.Slice(keys, func(i, j int) bool { return keys[i] < keys[j] })
+		// 	for _, k := range keys {
+		// 		fmt.Println("Depth", k)
+		// 		d.Draw(gridMap[k])
+		// 	}
+		// 	fmt.Println("# bugs:", d.numBugs(gridMap))
+		// }
+
+		for depth, grid := range gridMap {
+			for i, r := range grid {
+				for j := range r {
+					if i == 2 && j == 2 {
+						continue
+					}
+					numActivated := d.recursiveCalcActivatedNeighbors(gridMap, depth, i, j)
+					if grid[i][j] {
+						scratchMap[depth][i][j] = numActivated == 1
+					} else {
+						scratchMap[depth][i][j] = numActivated == 1 || numActivated == 2
+					}
+				}
+			}
+		}
+
+		for d := range gridMap {
+			copy2d(gridMap[d], scratchMap[d])
+		}
+	}
+
+	return fmt.Sprintf("Bugs present after 200 minutes: %s%d%s", u.TextBold, d.numBugs(gridMap), u.TextReset)
+}

inputs/20p.txt

@@ -0,0 +1,113 @@
+                                   G           R   U       E         Z S       S                                       
+                                   W           N   C       K         Z G       D                                       
+  #################################.###########.###.#######.#########.#.#######.#####################################  
+  #.#.......#.#.........#.#.#.....#.#.....#.#.#...#.....#.........#.....#...#.#...........#.......#.....#.....#.#...#  
+  #.#####.###.###.###.#.#.#.###.###.#.###.#.#.###.#.###.###.#####.#.###.###.#.###.#########.###.###.#######.###.#.###  
+  #.#.#.#...#...#.#.#.#.................#.#...#...#.#.#...#.#.....#.#.#.#.....................#.#.......#.........#.#  
+  #.#.#.#.###.#####.#########.###########.#.#.#.###.#.#######.###.#.#.#####.###.#.###.#.###.#.###.#######.#######.#.#  
+  #...#...#.#.#.#.........#...#...#.......#.#...#.......#.....#.#.#.....#.....#.#...#.#.#...#.#...#.#.........#.#.#.#  
+  #.#.###.#.#.#.#####.#.#.#######.#.#######.###.#.###.#####.###.#####.#.###.#########.#.#.#######.#.#####.#####.#.#.#  
+  #.#...#.#.#.#.#.....#.#.................#.#...#.#.#.....#...#.#.#...#...#.#.....#.#.#.#...#.#.#...........#.#.....#  
+  ###.###.#.#.#.#.#.#####.#.###.#########.#.#######.#.#####.###.#.#.#.#####.#.#.###.#.#######.#.#.###.#######.###.#.#  
+  #...#.......#...#.#.#.#.#...#.#.........#.....#.......#.#.......#.#...#.....#.....#.#...#.........#...#.#.#.#.#.#.#  
+  ###.#######.#######.#.###########.#.#####.###.#####.###.#.#####.#.###.#.#.###.#.#######.###.#####.#####.#.#.#.#####  
+  #.......#.#...#.......#.........#.#.#...#.#.#.#.....#.....#...#.#...#.#.#.#...#...#...#...#...#.#.#...........#.#.#  
+  #.#.###.#.#.#########.#########.#.###.###.#.#####.#.###.#.#.#.#.#.###########.#.###.###.###.###.###.###.#.#####.#.#  
+  #.#...#.....#.#...#.#.#.#.#.............#.....#...#...#.#.#.#...#...#.#.#.....#.........#...#.......#...#...#...#.#  
+  ###########.#.#.###.#.#.#.#######.#####.#.#####.#.#######.#####.###.#.#.#####.#.#.###.#####.###.#############.#.#.#  
+  #.#.#.#.#.....#.#.....#.#.#.#.....#...#.#.....#.#.....#...#.#.#...#...#.#.#...#.#...#...#...#...#...#.#.......#.#.#  
+  #.#.#.#.###.###.#####.#.#.#.#####.#.###.#.#########.#######.#.#.###.###.#.#.###.###.#####.#####.#.###.#####.#####.#  
+  #.#...#.#...#.#.#...#...#.#.....#.#.....#.#...#.....#.......#.#.#...#.....#.#.#.#.......#.......#...#.#.#...#.#...#  
+  #.#.#.#.###.#.#.###.#.###.#.#####.#.###.#.###.###.###.#.#.###.#.#.###.#.#.###.#.###.#####.#.#####.###.#.###.#.###.#  
+  #.#.#.#.#...#.#...#...#.#.#...#...#...#.#.#.....#.#...#.#.#.....#.#...#.#.#.......#.......#...#.#.....#.........#.#  
+  #.#.###.###.#.#.#####.#.#.#.###.#.#####.#.#.###.#.###.#.###.#.###.#.###.#####.#####.#####.#####.###.#########.#.#.#  
+  #.....#...#.......#.#.#.......#.#.#...#.#...#.#.#.....#...#.#...#...#.#...#.......#...#.#...#...#...#.#.#.#.#.#.#.#  
+  ###.###.#######.###.#.#.#.#.#########.#.#####.#.#.#####.#######.#####.#.#####.#.#.###.#.#######.###.#.#.#.#.#.###.#  
+  #.....#...#.#.#.......#.#.#.#.#.......#...#.....#.#.....#.......#.......#.#...#.#.#.#...#.....#.#.....#.#.#...#.#.#  
+  ###.###.###.#.#######.#.#####.#####.#.#.###.#########.#.###.#.#####.#####.###.#####.#######.###.###.###.#.#.###.#.#  
+  #.....#.......#...#...#...#.#.#.#.#.#.#.#.......#.#...#.#.#.#...#.......#...#.......#...#.....#...#.#.........#...#  
+  #.#####.#######.###.#.#.###.#.#.#.#.#.#.###.#.###.#.#####.#####.#####.#####.###.#######.###.###.###.#########.#.###  
+  #...#...#...#.#.#...#.#.#.#.........#.....#.#.....#.......#.......#...#.............#...#...#.#.........#...#.#...#  
+  #.###.###.###.#.#####.#.#.#.#####.#############.#######.#####.#####.#######.###########.###.#.###.#######.###.#.###  
+  #...#...#...#...#.#...#...#.#    S             L       B     V     G       R          #.#.#.#.....#.#.......#.#...#  
+  #.###.#.#.#####.#.###.#.###.#    D             M       E     H     X       Q          #.#.#.#####.#.###.#####.#.###  
+  #.....#.#.................#.#                                                         #.........................#.#  
+  #.###.###.#####.#.#.#.###.###                                                         #.#.#.###.#######.###.#.#.#.#  
+  #.#.#.....#.#...#.#.#.#.....#                                                       RZ..#.#...#.....#.#...#.#.#.#..BE
+  #.#.#####.#.#####.#.#####.###                                                         #######.#####.#.#.#######.#.#  
+  #.....#.#.....#.#.#.....#.#.#                                                         #.#.#.#.#.#...#.......#...#.#  
+  ###.###.###.#.#.#.#.###.#.#.#                                                         #.#.#.###.#####.#.#######.#.#  
+RI....#.....#.#.#...#.#.#.#....UW                                                       #.#.......#...#.#.#.#...#...#  
+  #####.###############.###.###                                                         #.###.#####.#.#####.#.#.#####  
+  #.....#.#.#...#.#.....#.#...#                                                       GW..........#.#.........#.#...#  
+  #.###.#.#.#.###.###.###.#####                                                         #.###.#.#.###.#######.###.###  
+  #...#...#.....#.#.......#....FM                                                       #.#...#.#.....#...#.........#  
+  ###.###.#.#.#.#.#.#########.#                                                         ###.#######.###.###########.#  
+AJ..#...#...#.#...#...#.....#.#                                                         #...#.#.#...#...#.#...#.#.#..GX
+  #.#.#########.#.#.#######.#.#                                                         #####.#.#######.#.###.#.#.###  
+  #.....#.#.#.#.#.............#                                                         #...............#...#........DD
+  #######.#.#.###########.###.#                                                         ###.#######.###.#.#.#.#.###.#  
+  #.....................#.#...#                                                         #.......#.....#...#.#.#.#...#  
+  ###.###.#.#.###.#####.#######                                                         #####.#########.###.#.###.###  
+GP..#...#.#.#.#.....#.#...#...#                                                       SG..#...#.....#...#.#.....#...#  
+  #.###.#####.#.#.#.#.###.###.#                                                         #.#.###.#.#######.#######.###  
+  #.#.....#.#.#.#.#.#.....#...#                                                         #.....#.#.#.#...#.#.#...#.#.#  
+  #.#.#####.#########.#######.#                                                         #########.#.###.#.#.#.#####.#  
+  #.....#...#..................SI                                                     DD....#........................UW
+  #.#######.#####.###.###.#####                                                         #.###.#####.#.###.#.###.#####  
+  #.#.#...#...#.....#.#.#.#.#..AJ                                                       #.........#.#.#.#.#.#.....#.#  
+  ###.#.###.#.#########.###.#.#                                                         #.#####.###.#.#.#######.###.#  
+  #.........#.#...#.....#.#.#.#                                                         #...#.....#.#...#.#.#.#.#....LM
+  #########.#.###.#.###.#.#.#.#                                                         #########.#.#.###.#.#.#####.#  
+AA......#.#.#.....#.#...#.....#                                                         #.#.#.#.#.#.#.#...#.#.#.....#  
+  #.#####.#.#.###.#.#.###.#.###                                                         #.#.#.#.#########.#.#.#####.#  
+JO..........#...#...#.....#...#                                                         #.#.......#.#.............#.#  
+  #####.###############.###.#.#                                                         #.#.#.#####.###.###.#.###.#.#  
+  #.#.#...#.........#.#.#.#.#.#                                                       TX....#.............#.#...#...#  
+  #.#.#######.#.#.#.#.###.###.#                                                         #.###.#.###.#####.###########  
+VH......#.....#.#.#.....#...#.#                                                         #.#...#.#...#...#.#.....#...#  
+  #####.#.###########.###.#####                                                         #############.#####.###.#.#.#  
+  #.....#.....#.#.......#.....#                                                         #.#...#...#.#.......#.#.#.#..RZ
+  #.#.#######.#.#######.#.#####                                                         #.###.###.#.###.#.###.#.#.###  
+  #.#...........#.#............FW                                                     RN..#.....#...#.#.#.#.....#...#  
+  #########.###.#.#.###########                                                         #.#.#.###.###.###.#.#####.###  
+  #...#...#.#.....#.#.........#                                                         #...#.............#.......#.#  
+  #.#.#.#################.#.#.#                                                         ###############.###########.#  
+AX..#...#.#...#.#...#...#.#.#..HR                                                     JO............#.#.#...........#  
+  #.#.###.###.#.#.#####.###.#.#                                                         #.#.#####.#.#.###.#.#.#####.#  
+TX..#...#.......#...#.....#.#..EK                                                       #.#...#.#.#.......#.#...#.#..MM
+  ###.#.###.#.#.#.#.###.#.#.###                                                         #.###.#.#######.#.###.###.#.#  
+  #...#.....#.#...#.....#.....#                                                         #.#.#.....#.#...#...#.#.....#  
+  #####.#.#.#####.###.#######.#        R     Y   G           U     A           M S      #.#.#.#.###.#####.#.#.###.#.#  
+  #.....#.#...#.....#.....#...#        I     Q   P           C     X           M Y      #...#.#.#.....#...#.#...#.#.#  
+  #####.#########.###.#####.###########.#####.###.###########.#####.###########.#.#######.#.###.#.#########.#.#####.#  
+  #...#...#.#.......#.....#...#...#.....#.....#.....#.#.....#...#...........#...#...#...#.#.#.....#.#.......#.#.....#  
+  #.#.#.###.###.#.#.#######.#####.###.###.###.#####.#.###.#.#.#########.#####.#####.#.#########.###.###.#####.###.#.#  
+  #.#.......#...#.#.#.......#.....#.#.#.....#.#.....#...#.#.......#.#.#...#.......#.#.......#.#.#.#.....#.......#.#.#  
+  #.#.#.#.#####.###########.#####.#.#.#.#.#.#####.###.###.#########.#.#.#######.###.#.#######.###.###.#.###.#.#.#.#.#  
+  #.#.#.#...#.......#.......#.........#.#.#.....#.#.....#.........#.........#.#.#.....#.......#.......#.#.#.#.#.#.#.#  
+  #######.#.#.#.#####.#.#########.#############.#.#.###.#######.#####.#.#####.#.#.#######.#####.#.#.###.#.#.#######.#  
+  #.......#.#.#...#...#.#.........#.......#...#.#.....#.#.......#.....#...#.....#...........#.#.#.#.#.....#...#.....#  
+  #.#.#.#####.#.#.#####.#.#######.#.###.###.###.#.###.#.#.###.#.#.#.###.#.#####.#.###.#.#.###.###.#.#.#.#####.#####.#  
+  #.#.#.#.....#.#.#.....#...#.#.....#...#.......#.#...#.#...#.#.#.#...#.#.#.....#.#...#.#.......#.#.#.#...#.#.#.....#  
+  #.###.###.#.###.###.#.#.###.#.#.#.#.###.###.#.#######.###.#.###.#######.#.#.#.#####.#.#.#.#############.#.#####.###  
+  #.#.#.#.#.#...#.#...#.#.#.....#.#.#...#...#.#...#.....#...#...#...#.....#.#.#.....#.#.#.#.#.....#.#.#.......#...#.#  
+  ###.#.#.#.#.###.#####.#############.#.#.#.#.#######.###.###.###.#############.#####.#####.###.###.#.#.#####.###.#.#  
+  #.......#.#.#.....#...#.#.......#...#.#.#.#.#.#.#.#...#...#.#.....#.#.#...#.....#.#.#...#...#.......#.....#...#...#  
+  ###.###.#.###.#########.#######.#####.#.#####.#.#.#.###.#######.###.#.#.#####.###.#.#.###.###.#####.#.#.###.###.###  
+  #.....#.#.#.....#.....#.#.......#.#.#.#...#.......#.#.......#...#.....#.......#.........#.#.#.....#.#.#.#...#.....#  
+  #.#####.#.###.#.#####.#.#######.#.#.#.#.#######.#.#.###.#####.#.###.#.###.#.#####.###.#####.#.#######.###.#.#.#.###  
+  #.#.....#.#...#...#.......#.#.....#...#.#.#.....#...#.......#.#.....#.#...#...#.#...#...#.#.#.....#.#.#.#.#.#.#...#  
+  #####.#.#.###.#######.#.###.###.#.#.###.#.#####.#######.#######.#.#####.###.###.###.#####.#.#.#####.###.#######.#.#  
+  #.#.#.#.#.#.#.#...#...#...#.#.#.#...#.......#.#.....#.#.#...#...#.....#.#.......#.........#.#...#.#.........#.#.#.#  
+  #.#.#######.#####.#####.###.#.#.#########.###.#####.#.#.#.#######.#########.#.###.#########.###.#.#.#########.#.#.#  
+  #...#.#.#.#.....#.#...................#...#...#...#...#.....#...#.#...#...#.#.#.....#.#.......#.#.#.#.#.#.#...#.#.#  
+  ###.#.#.#.#.###.#.#####.#############.###.#.#.#.#.###.#.#.#####.#.#.#####.###.#.###.#.#####.###.#.#.#.#.#.###.#.###  
+  #...........#.#.#...#...#.#.......#.#...#...#.#.#...#.#.#...#.#.......#.....#.#...#.#.#.#.#.....#.....#.#.....#...#  
+  #####.#.#.#.#.###.#####.#.#.#.###.#.#.#######.#.###.#.#.###.#.#####.###.###.#.#.###.#.#.#.#.#####.###.#.#.#########  
+  #.#...#.#.#.............#...#...#...#.....#...#...#...#.#.#.#...#...#...#.#...#.#...................#.............#  
+  #.#####.#######.#.###.###.#.#.#####.#.#######.###.#####.#.###.#.#.#####.#.###.#.#.#####.###.#####.###.#.###.#.#####  
+  #.......#.......#...#...#.#.#.#.........#.....#.....#.......#.#.......#.....#.#.#.....#...#.....#...#.#...#.#.....#  
+  ###################################.#######.###.#########.#######.#########.#######.###############################  
+                                     Y       S   R         S       F         F       H                                 
+                                     Q       Y   Q         I       M         W       R                                 

inputs/20s1.txt

@@ -0,0 +1,19 @@
+         A           
+         A           
+  #######.#########  
+  #######.........#  
+  #######.#######.#  
+  #######.#######.#  
+  #######.#######.#  
+  #####  B    ###.#  
+BC...##  C    ###.#  
+  ##.##       ###.#  
+  ##...DE  F  ###.#  
+  #####    G  ###.#  
+  #########.#####.#  
+DE..#######...###.#  
+  #.#########.###.#  
+FG..#########.....#  
+  ###########.#####  
+             Z       
+             Z       

inputs/20s2.txt

@@ -0,0 +1,37 @@
+                   A               
+                   A               
+  #################.#############  
+  #.#...#...................#.#.#  
+  #.#.#.###.###.###.#########.#.#  
+  #.#.#.......#...#.....#.#.#...#  
+  #.#########.###.#####.#.#.###.#  
+  #.............#.#.....#.......#  
+  ###.###########.###.#####.#.#.#  
+  #.....#        A   C    #.#.#.#  
+  #######        S   P    #####.#  
+  #.#...#                 #......VT
+  #.#.#.#                 #.#####  
+  #...#.#               YN....#.#  
+  #.###.#                 #####.#  
+DI....#.#                 #.....#  
+  #####.#                 #.###.#  
+ZZ......#               QG....#..AS
+  ###.###                 #######  
+JO..#.#.#                 #.....#  
+  #.#.#.#                 ###.#.#  
+  #...#..DI             BU....#..LF
+  #####.#                 #.#####  
+YN......#               VT..#....QG
+  #.###.#                 #.###.#  
+  #.#...#                 #.....#  
+  ###.###    J L     J    #.#.###  
+  #.....#    O F     P    #.#...#  
+  #.###.#####.#.#####.#####.###.#  
+  #...#.#.#...#.....#.....#.#...#  
+  #.#####.###.###.#.#.#########.#  
+  #...#.#.....#...#.#.#.#.....#.#  
+  #.###.#####.###.###.#.#.#######  
+  #.#.........#...#.............#  
+  #########.###.###.#############  
+           B   J   C               
+           U   P   P               

inputs/20s3.txt

@@ -0,0 +1,37 @@
+             Z L X W       C                 
+             Z P Q B       K                 
+  ###########.#.#.#.#######.###############  
+  #...#.......#.#.......#.#.......#.#.#...#  
+  ###.#.#.#.#.#.#.#.###.#.#.#######.#.#.###  
+  #.#...#.#.#...#.#.#...#...#...#.#.......#  
+  #.###.#######.###.###.#.###.###.#.#######  
+  #...#.......#.#...#...#.............#...#  
+  #.#########.#######.#.#######.#######.###  
+  #...#.#    F       R I       Z    #.#.#.#  
+  #.###.#    D       E C       H    #.#.#.#  
+  #.#...#                           #...#.#  
+  #.###.#                           #.###.#  
+  #.#....OA                       WB..#.#..ZH
+  #.###.#                           #.#.#.#  
+CJ......#                           #.....#  
+  #######                           #######  
+  #.#....CK                         #......IC
+  #.###.#                           #.###.#  
+  #.....#                           #...#.#  
+  ###.###                           #.#.#.#  
+XF....#.#                         RF..#.#.#  
+  #####.#                           #######  
+  #......CJ                       NM..#...#  
+  ###.#.#                           #.###.#  
+RE....#.#                           #......RF
+  ###.###        X   X       L      #.#.#.#  
+  #.....#        F   Q       P      #.#.#.#  
+  ###.###########.###.#######.#########.###  
+  #.....#...#.....#.......#...#.....#.#...#  
+  #####.#.###.#######.#######.###.###.#.#.#  
+  #.......#.......#.#.#.#.#...#...#...#.#.#  
+  #####.###.#####.#.#.#.#.###.###.#.###.###  
+  #.......#.....#.#...#...............#...#  
+  #############.#.#.###.###################  
+               A O F   N                     
+               A A D   M                     

inputs/22p.txt

@@ -0,0 +1,100 @@
+deal into new stack
+cut -2732
+deal into new stack
+deal with increment 57
+cut 5974
+deal into new stack
+deal with increment 32
+cut -1725
+deal with increment 24
+cut 6093
+deal with increment 6
+cut -2842
+deal with increment 14
+cut 2609
+deal with increment 12
+cut -6860
+deal with increment 51
+cut -6230
+deal with increment 61
+cut 3152
+deal with increment 28
+cut 2202
+deal into new stack
+deal with increment 60
+cut 433
+deal into new stack
+cut -6256
+deal with increment 13
+deal into new stack
+cut 8379
+deal into new stack
+deal with increment 54
+cut 1120
+deal with increment 16
+cut -5214
+deal with increment 63
+deal into new stack
+cut -8473
+deal with increment 11
+cut 228
+deal with increment 45
+cut -6755
+deal with increment 50
+cut -3391
+deal with increment 44
+cut -1341
+deal with increment 28
+cut -6788
+deal with increment 52
+cut 3062
+deal with increment 41
+cut 4541
+deal with increment 57
+cut -7962
+deal with increment 56
+cut 9621
+deal with increment 57
+cut 3881
+deal with increment 36
+deal into new stack
+deal with increment 45
+cut 522
+deal with increment 9
+deal into new stack
+deal with increment 60
+deal into new stack
+deal with increment 12
+cut -9181
+deal with increment 63
+deal into new stack
+deal with increment 14
+cut -2906
+deal with increment 10
+cut 848
+deal with increment 75
+cut 798
+deal with increment 29
+cut 1412
+deal with increment 10
+deal into new stack
+cut -5295
+deal into new stack
+cut 4432
+deal with increment 72
+cut -7831
+deal into new stack
+cut 6216
+deal into new stack
+deal with increment 7
+cut -1720
+deal into new stack
+cut -5465
+deal with increment 70
+cut -5173
+deal with increment 7
+cut 3874
+deal with increment 65
+cut 921
+deal with increment 8
+cut -3094

inputs/22s1.txt

@@ -0,0 +1,3 @@
+deal with increment 7
+deal into new stack
+deal into new stack

inputs/22s2.txt

@@ -0,0 +1,3 @@
+cut 6
+deal with increment 7
+deal into new stack

inputs/22s3.txt

@@ -0,0 +1,3 @@
+deal with increment 7
+deal with increment 9
+cut -2

inputs/22s4.txt

@@ -0,0 +1,10 @@
+deal into new stack
+cut -2
+deal with increment 7
+cut 8
+cut -4
+deal with increment 7
+cut 3
+deal with increment 9
+deal with increment 3
+cut -1

inputs/24p.txt

@@ -0,0 +1,5 @@
+##..#
+...##
+.#.##
+#..#.
+..#..

inputs/24s1.txt

@@ -0,0 +1,5 @@
+....#
+#..#.
+#..##
+..#..
+#....

inputs/24s2.txt

@@ -0,0 +1,5 @@
+.....
+.....
+.....
+#....
+.#...

main.go

@@ -53,6 +53,11 @@ var dayMap = []day{
 	&days.Day17{},
 	&days.Day18{},
 	&days.Day19{},
+	&days.Day20{},
+	&days.Day21{},
+	&days.Day22{},
+	&days.Day23{},
+	&days.Day24{},
 }
 
 func main() {

utilities/intcode.go

@@ -28,6 +28,8 @@ type IntcodeProgram struct {
 	program       []int64
 	relativeBase  int
 	haltRequested bool
+	printASCII    bool
+	feedInput     []rune
 }
 
 type IntcodeProgramState struct {
@@ -140,14 +142,15 @@ func (p *IntcodeProgram) Reset() {
 	p.relativeBase = 0
 }
 
-func (p *IntcodeProgram) Run() {
+func (p *IntcodeProgram) Run() int64 {
-	p.RunIn(func(int) int64 { return 0 }, func(int64, IntcodeProgramState) {})
+	return p.RunIn(func(int) int64 { return 0 }, func(int64, IntcodeProgramState) {})
 }
 
-func (p *IntcodeProgram) RunIn(inputFunc ProvideInputFunc, outputFunc ReceiveOutputFunc) {
+func (p *IntcodeProgram) RunIn(inputFunc ProvideInputFunc, outputFunc ReceiveOutputFunc) int64 {
 	p.init()
 
 	inputsRequested := 0
+	lastOutput := int64(0)
 	for instructionPointer := 0; instructionPointer < len(p.program) && !p.haltRequested; {
 		instruction := p.GetMemory(instructionPointer)
 		instructionPointer++
@@ -184,13 +187,28 @@ func (p *IntcodeProgram) RunIn(inputFunc ProvideInputFunc, outputFunc ReceiveOut
 		case opInput:
 			inputsRequested++
 			param1 := p.GetMemory(instructionPointer)
-			p.setMemory(int(param1), inputFunc(inputsRequested), paramModes[0])
+			var inputVal int64
+			if len(p.feedInput) > 0 {
+				inputVal = int64(p.feedInput[0])
+				p.feedInput = p.feedInput[1:]
+			} else {
+				inputVal = inputFunc(inputsRequested)
+			}
+			if p.printASCII && inputVal <= 255 {
+				fmt.Printf("%c", rune(inputVal))
+			}
+			p.setMemory(int(param1), inputVal, paramModes[0])
 
 			instructionPointer += 1
 
 		case opOutput:
 			param1 := p.GetMemory(instructionPointer)
-			outputFunc(p.getParamValue(int(param1), paramModes[0]), p.makeState(instructionPointer))
+			param1Val := p.getParamValue(int(param1), paramModes[0])
+			if p.printASCII && param1Val <= 255 {
+				fmt.Printf("%c", rune(param1Val))
+			}
+			outputFunc(param1Val, p.makeState(instructionPointer))
+			lastOutput = param1Val
 
 			instructionPointer += 1
 
@@ -256,8 +274,19 @@ func (p *IntcodeProgram) RunIn(inputFunc ProvideInputFunc, outputFunc ReceiveOut
 	}
 
 	p.haltRequested = false
+
+	return lastOutput
 }
 
 func (p *IntcodeProgram) Stop() {
 	p.haltRequested = true
 }
+
+func (p *IntcodeProgram) SetDebugASCIIPrint(enable bool) {
+	p.printASCII = enable
+}
+
+func (p *IntcodeProgram) FeedInputString(str string) {
+	p.feedInput = make([]rune, len(str))
+	copy(p.feedInput, []rune(str))
+}