Day 19 solution

I had some trouble with the logic of this puzzle in my head, and the visuals were too large to realistically render for me to spot-check my solution, so I kept getting part 2 wrong. I eventually realized what needed to be done to get the right answer, which was partially the realization that I needed to check +99 instead of +100, and partially that I probably didn't need to check the entire space, just the bounding points (although I'm not entirely certain this is fully correct - I feel like I've seen some rows where a row below is shorter than a row above, which won't work with my solution here).

And then I optimized it with a bisect instead of a linear search. I think the bounds could be narrowed down, but I don't actually know what the min/max values are for all programs, and this is fast enough, so I'm leaving it alone. I'm not even sure that 2500 is a reasonable "too large" high end, honestly.

days/14.go

@@ -104,26 +104,10 @@ func (d *Day14) Part1() string {
 func (d *Day14) Part2() string {
 	oreAvailable := int64(1000000000000)
 	estimate := oreAvailable / d.getOreRequiredForFuel(1)
-
-	high := estimate * 2
-	low := estimate
-
-	lastSuccess := low
-	lastFailure := high
-	fuelProduced := low
-
-	for math.Abs(float64(lastFailure-lastSuccess)) > 1 {
-		oreConsumed := d.getOreRequiredForFuel(fuelProduced)
-		adjustment := (lastFailure - lastSuccess) / 2
-		if oreConsumed < oreAvailable {
-			lastSuccess = fuelProduced
-		} else {
-			lastFailure = fuelProduced
-			adjustment = -adjustment
-		}
-
-		fuelProduced += adjustment
-	}
+	lastSuccess := u.Bisect(estimate, estimate*2, 1, func(val int64) bool {
+		oreConsumed := d.getOreRequiredForFuel(val)
+		return oreConsumed < oreAvailable
+	})
 
 	return fmt.Sprintf("Maximum fuel we can make from 1 trillion ore: %s%d%s", u.TextBold, lastSuccess, 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 reachableKeysMemo struct {
+	pos       rune
+	keysFound int
+}
+
+type minStepsMemo struct {
+	pos        string
+	keysToFind int
+	keysFound  int
+}
+
+type Day18 struct {
+	entrance           day18Vec
+	grid               [][]day18Cell
+	doors              map[day18Vec]int
+	keys               map[day18Vec]int
+	knownReachableKeys map[reachableKeysMemo][]u.Pair[rune, int]
+	knownMinimumSteps  map[minStepsMemo]int
+}
+
+func (d *Day18) Parse() {
+	d.doors = make(map[day18Vec]int)
+	d.keys = make(map[day18Vec]int)
+	d.knownReachableKeys = make(map[reachableKeysMemo][]u.Pair[rune, int])
+	d.knownMinimumSteps = make(map[minStepsMemo]int, 0)
+
+	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 day18PriorityQueueHeap []day18PriorityQueue
+
+func (h day18PriorityQueueHeap) Len() int           { return len(h) }
+func (h day18PriorityQueueHeap) Less(i, j int) bool { return h[i].distance < h[j].distance }
+func (h day18PriorityQueueHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
+
+func (h *day18PriorityQueueHeap) Push(x any) {
+	*h = append(*h, x.(day18PriorityQueue))
+}
+
+func (h *day18PriorityQueueHeap) Pop() any {
+	old := *h
+	n := len(old)
+	x := old[n-1]
+	*h = old[0 : n-1]
+	return x
+}
+
+func (d Day18) reachableKeys(inPos rune, keysFound int, graph day18Graph) []u.Pair[rune, int] {
+	memo := reachableKeysMemo{
+		pos:       inPos,
+		keysFound: keysFound,
+	}
+	if v, exists := d.knownReachableKeys[memo]; exists {
+		return v
+	}
+
+	ret := make([]u.Pair[rune, int], 0)
+	distance := make(map[rune]int)
+
+	ih := make(day18PriorityQueueHeap, 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,
+				})
+			}
+		}
+	}
+
+	d.knownReachableKeys[memo] = ret
+	return ret
+}
+
+func (d Day18) minimumSteps(inPos string, keysToFind int, keysFound int, graph day18Graph) int {
+	memo := minStepsMemo{
+		pos:        inPos,
+		keysToFind: keysToFind,
+		keysFound:  keysFound,
+	}
+	if v, exists := d.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)
+			}
+		}
+	}
+
+	d.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
+	d.knownMinimumSteps = make(map[minStepsMemo]int)
+	d.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)
+}

days/19.go

@@ -0,0 +1,122 @@
+package days
+
+import (
+	"fmt"
+
+	u "parnic.com/aoc2019/utilities"
+)
+
+type Day19 struct {
+	program u.IntcodeProgram
+}
+
+func (d *Day19) Parse() {
+	d.program = u.LoadIntcodeProgram("19p")
+}
+
+func (d Day19) Num() int {
+	return 19
+}
+
+func (d *Day19) Part1() string {
+	grid := make([][]bool, 50)
+	for y := 0; y < len(grid); y++ {
+		grid[y] = make([]bool, 50)
+	}
+
+	count := int64(0)
+
+	for y := 0; y < 50; y++ {
+		for x := 0; x < 50; x++ {
+			d.program.Reset()
+			d.program.RunIn(func(inputStep int) int64 {
+				if inputStep == 1 {
+					return int64(x)
+				}
+
+				return int64(y)
+			}, func(val int64, state u.IntcodeProgramState) {
+				res := val == 1
+				grid[y][x] = res
+				if res {
+					count++
+				}
+			})
+		}
+	}
+
+	// fmt.Println("50x50 tractor view:")
+	// for y := 0; y < len(grid); y++ {
+	// 	for x := 0; x < len(grid[y]); x++ {
+	// 		if grid[y][x] {
+	// 			fmt.Print("█")
+	// 		} else {
+	// 			fmt.Print(" ")
+	// 		}
+	// 	}
+	// 	fmt.Println()
+	// }
+
+	return fmt.Sprintf("Points affected in 50x50 area: %s%d%s", u.TextBold, count, u.TextReset)
+}
+
+func (d *Day19) Part2() string {
+	f := func(x, y int) bool {
+		ret := false
+		d.program.Reset()
+		d.program.RunIn(func(inputStep int) int64 {
+			if inputStep == 1 {
+				return int64(x)
+			}
+			return int64(y)
+		}, func(val int64, state u.IntcodeProgramState) {
+			ret = val == 1
+		})
+
+		return ret
+	}
+
+	// find lower bound
+	startY := 0
+	startX := 0
+	for y := 1; startY == 0; y++ {
+		for x := 0; x < 10*y; x++ {
+			if f(x, y) {
+				startY = y
+				startX = x
+				break
+			}
+		}
+	}
+
+	lastGoodX := 0
+	threshold := 1
+	y := u.Bisect(startY+100, 2500, threshold, func(y int) bool {
+		foundX := false
+		for x := startX; ; x++ {
+			if !f(x, y) {
+				if !foundX {
+					continue
+				} else {
+					return true
+				}
+			}
+			if !foundX {
+				foundX = true
+			}
+
+			if !f(x+99, y) {
+				return true
+			}
+			if !f(x, y+99) {
+				continue
+			}
+
+			lastGoodX = x
+			return false
+		}
+	})
+
+	result := (lastGoodX * 10000) + y
+	return fmt.Sprintf("Closest 100x100 square for the ship starts at %d,%d = %s%d%s", lastGoodX, y, u.TextBold, result, 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/18p.txt

@@ -0,0 +1,81 @@
+#################################################################################
+#...............#.......#...............#.........#.......#.......#.....#.......#
+#.#########.#.###.#####.#.#.#######.#####.#######.#.#######.#.###.###.#.#.#####.#
+#.#.#.....#.#.#...#...#..f#...#.....#...#...#.....#.........#...#.....#...#m....#
+#.#.#.###.###.#.#####.#######.#######.#.#.#.#.#######.#########.###########.#####
+#...#...#.#...#.......#.....#.#.......#.#.#.#...#...#...#.......#..h......#.....#
+###.###.#.#.#########.#.###.#T#.#######.###.###.#B#.#.###.#######.#######.#####.#
+#...#...#...#.....#...#...#.#...#.....#.#...#.#...#.#.#...#.........#...#.......#
+#####.#######.###.#.###.#.#######.###.#.#.###.#####.###.#.###########.#.#######.#
+#...#...#.....#.#...#.#.#.....#...#.....#.#.....#...#...#.#...........#.#.....#.#
+#.#.###.#.#####.#####.#.#####.#.###.#####.#.###.#.###.#####.###########.#.###.#.#
+#.#.....#.#.....#.........#...#...#.#...#.#...#..x#...W.....#.....#.....#.#...#.#
+#.#######.###.#.#########.#.#####.###.#.#.###.#######.#######.###.#.#####.#.#####
+#.........#...#.......#.#.#.#...#.....#.#.#.#.#.....#...#.....#...#.#.....#.....#
+#.#########O#########.#.#.#.#.#.#.#####.#.#.#.###.#.#.###.#####.###.#.#########.#
+#.#.........#.........#...#.#.#.#...#.#.#.#.......#.#.#...#...#.#.......#.....#.#
+#.#####.#########.#########.#.#.###.#.#.#.#########.###.###.###.#####.###.###.#.#
+#.....#...#.....#.#.........#.#.#.....#.#.....#.....#...#...........#.#...#e..#.#
+#####.###.#K###.#.#####.#####.#.#######.#####.#####.#.#.###########.###.###.###.#
+#...#.....#.#...#.......#.....#.#.......#.....#...#...#.#.........#.....#.#.#...#
+#.#####.###.#.#########.#.#####.#.#####.#.#####.#.#######.#####.#.#######.#.#.#.#
+#.#j..#.#...#a..#.....#.#.#.......#.....#.......#...........#.#.#.......#.#...#.#
+#.#.#.#.#.#####.#.#####.#.#############.#.###################.#########.#.#####.#
+#...#.#.#.#...#...#.....#.#..z..#.....#.#.....#.......#.....#...#...#...#...#...#
+#.###.#.#.###.#####.#####.#.###.#.###.#######.#.#.#####.###.###.#.#.#.###.###.###
+#.#...#.#.....#.#...#...#.#...#.#.#.#...#.....#.#.....#...#.....#.#...#.#...#...#
+###.###.#####.#.#.###.#.#.###.#.#.#.###.#.###########.###.#######.#####.#.#.###.#
+#...#...#...#.#.......#.#.....#.#.....#.#.#.............#...#...#...#.....#.#...#
+#.#.#.#####.#.#############.###.###.###.#.#.#########.#####.###.#.#.#####.#.#.###
+#.#.#.#.....#.............#...#.....#...#.#.....#...#.#.....#...#.#.#...#.#.#.#.#
+#.###.#.#.###############.###.#####.#.#.#.#####.#.#.#.#.#####.###.#.#.#.#.#.#.#.#
+#.#...#.#.......#.........#...#...#.#.#.#.#.....#.#...#.#.........#.#.#.#.#...#.#
+#.#.#######.###.#.#########.###.#.###.#.#.#.###########.#.#########.#.#.#####.#.#
+#.#.......#...#.#.#.......#...#.#.#...#.#.#...#.......#.#.#.......#...#.#...#c..#
+#.#######.#.#.###.###.###.#####.#.#.###.#.###.#.#####.#.###.#####.#.###.#.#.###.#
+#.L..q..#.#.#...#...#.#.#.....#.#...#...#...#.....#...#.....#.....#...#...#.#...#
+#.#######.#####.###.#.#.#####.#.#####.#####.#######S#########.#############.#.###
+#...#...#.#.......#...#.#.....#.#...#...#...#.....#.....#...#.#.....#.....#k#...#
+#.#.#.#.#.#.#####.#####.#.#####.#.#.###.#.###.###.###.#.###.#.#.###.#.###.#.###.#
+#.#...#.....#...........#.......#.#...........#.......#.....#...#.....#.....#...#
+#######################################.@.#######################################
+#.#...#...........#u....#...#.......#...............#.....#...................#.#
+#.#.#.#.#####.###.#.#.#.#.#.#.#.#####.#.#####.#####.#.###.#.###.#############.#.#
+#.#.#...#...#...#.#.#.#.#.#...#.#s....#.#.....#...#.#.#.#..p#.#.#.....#.....#...#
+#.#.#######.###.###.#.###.#####.#.#####.#.#######.#.#.#.#####.#.#.###.#.###.###.#
+#...#.........#.#...#.#...#...#...#...#.#...#.....#...#.......#.#.#.#.....#.#.#.#
+#.###.#.#####.#.#.###.#.###.#######.#.#.#.#.#.###.#####.#######.#.#.#######.#.#.#
+#...#.#.#.....#...#...#.#...#.....#.#...#.#.#.#...#.....#.......#.#...#.V...#...#
+###.###.#.#########.###.#.#.#.###.#.###.###.#.#####.#.###.#######.###.#.#####.###
+#.#.....#.#.....#...#.....#.#...#...#...#...#.#.....#.......#...#.#...#.#.....#.#
+#.#######.#N#.#.#.#.#.#########.#.#######.###.#.#############.#.#.#.#.#.#.#####.#
+#.......#.#.#.#.#.#.#.#...#.....#.#.....#.#.........#.........#.#...#.#.#.....U.#
+#.#######.###.#.#.###.#.#P#.#######.###.#.###.#######.#########.#####.#.#######.#
+#.#.....#...#.#.#.....#.#...#.......#...#...#...#.....#.......#.......#.#...#...#
+#.#.###.###.#.#########.###.#.#######.#####.###.#.#####.###.###########.#.#.#.###
+#...#...#.#.#.#.....#...#...#.#.....#...#...#...#.......#...#.........#.#.#.#.#.#
+#.###.#.#.#.#.#.#.###.#######.#.###.###.#.#####.#####.#####.#.#######.#.#.#Q#.#.#
+#.#...#...#.#...#...#.....#...#.#...#...#.....#.....#.#.Yi#.#.#...#...#.#.#.#...#
+#.#.#######.###.###.#####.#.###.#.#.#.###.###.#######.#.#.#.#.###.#.###.#.#.###.#
+#.#.......#...#.#.....#...#.#...#.#.#...#.#...#.......#.#.#.#...#.....#.#.#.#...#
+#.#######.###.###.#.###.###.#####.#####.#.#.#.#.#######.#.#.###.#####.#.#.#.#####
+#.#.....#.....#...#.#.#.........#.....#.#.#.#.#.#...#...#.#.#.#.#...#...#.#.....#
+#.#.###.#######.#####.#########.#.#.###.#.#.#.#.#.###.###.#.#.#.#.#.#####.#####.#
+#.#.#.....#.........#.#.....#.#.#.#b#...#.#.#.#.#.#..y#.#.#.#.#.#.#...#...#.....#
+#.###.#####.#######.#.#.###.#.#.#.#.#.#####.###.#.#.###.#.###.#.#.###.#.###.###.#
+#.E.#....d..#.......#...#.#.#.#.#.#.#...#...#...#.#...#.#...I.#...#..l#.#...#...#
+###.#.#######.###########F#.#.#.###.###.#.#.#.###.###.#.#########.#.###.#.###J###
+#...#...#...#...........#...#.......#...#.#.#.#.....#.G.#.......#.#.....#.#.#.#.#
+#.#####.#.#########.#.#.#.#########.#.#.#.###.#####.###.#.###.#.#####.###.#.#.#.#
+#..v..#...#.......#.#.#.#.#...#.....#.#.#...#.......#.#.#...#.#.....#.#...#.#...#
+#####.#####.#####.###.###.#.#.#.#####.#.#Z#.#######X#.#.#####.#####.#.#.###.###.#
+#...#.....#...#.....#...#...#.#.#...#.#.#.#.......#...#.....#.....#.#.#.#...#...#
+#.#######.#.#.#####.###.#####.#.#.###.#.###.#.#####.#######.#.###.#.###.#.###.###
+#.........#.#.#...#...#...#...#...#...#.#...#.#...#.#.R....g#.#...#.....#.#...#.#
+#.###########.#.#.###.###.#.###.###.###.#.#####.#.#.#.#########.#########.#.###.#
+#...#.#.....#...#.#.#.#...#..t#.#...#...#.#.....#...#...#.....#.#..n....#.M.#...#
+###.#.#.#.#.#####.#.#.#.#####.###.#####.#.#.###########.#.###.#.#.#######.###.#.#
+#...#...#.#.#..w#.#.#.#.....#...#.....#.#.#.......#.....#.#...#.#.#.D...#.....#.#
+#C#######.#.#.#.#.#.#.###.#.###.#####.#.#.#######.#.#####.#.###.#.#.###.#######H#
+#......o..#...#...#.......#...#.A.....#.#.........#r......#.....#.....#.........#
+#################################################################################

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 @@
+########################
+#...............b.C.D.f#
+#.######################
+#.....@.a.B.c.d.A.e.F.g#
+########################

inputs/18s4.txt

@@ -0,0 +1,9 @@
+#################
+#i.G..c...e..H.p#
+########.########
+#j.A..b...f..D.o#
+########@########
+#k.E..a...g..B.n#
+########.########
+#l.F..d...h..C.m#
+#################

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#
+#######

inputs/18s7.txt

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

inputs/18s8.txt

@@ -0,0 +1,7 @@
+#############
+#DcBa.#.GhKl#
+#.###...#I###
+#e#d#.@.#j#k#
+###C#...###J#
+#fEbA.#.FgHi#
+#############

inputs/18s9.txt

@@ -0,0 +1,9 @@
+#############
+#g#f.D#..h#l#
+#F###e#E###.#
+#dCba...BcIJ#
+#####.@.#####
+#nK.L...G...#
+#M###N#H###.#
+#o#m..#i#jk.#
+#############

inputs/19p.txt

@@ -0,0 +1 @@
+109,424,203,1,21102,11,1,0,1105,1,282,21101,0,18,0,1105,1,259,2101,0,1,221,203,1,21102,1,31,0,1105,1,282,21102,1,38,0,1105,1,259,20102,1,23,2,21201,1,0,3,21102,1,1,1,21102,57,1,0,1106,0,303,2102,1,1,222,21002,221,1,3,20101,0,221,2,21101,0,259,1,21101,0,80,0,1105,1,225,21101,44,0,2,21102,91,1,0,1105,1,303,1202,1,1,223,21002,222,1,4,21102,259,1,3,21102,1,225,2,21102,225,1,1,21101,118,0,0,1106,0,225,21002,222,1,3,21101,163,0,2,21101,0,133,0,1106,0,303,21202,1,-1,1,22001,223,1,1,21102,148,1,0,1106,0,259,1202,1,1,223,20101,0,221,4,21001,222,0,3,21102,1,24,2,1001,132,-2,224,1002,224,2,224,1001,224,3,224,1002,132,-1,132,1,224,132,224,21001,224,1,1,21101,195,0,0,105,1,108,20207,1,223,2,21002,23,1,1,21102,-1,1,3,21102,1,214,0,1106,0,303,22101,1,1,1,204,1,99,0,0,0,0,109,5,2101,0,-4,249,22102,1,-3,1,22101,0,-2,2,22101,0,-1,3,21102,250,1,0,1106,0,225,21202,1,1,-4,109,-5,2105,1,0,109,3,22107,0,-2,-1,21202,-1,2,-1,21201,-1,-1,-1,22202,-1,-2,-2,109,-3,2106,0,0,109,3,21207,-2,0,-1,1206,-1,294,104,0,99,22102,1,-2,-2,109,-3,2105,1,0,109,5,22207,-3,-4,-1,1206,-1,346,22201,-4,-3,-4,21202,-3,-1,-1,22201,-4,-1,2,21202,2,-1,-1,22201,-4,-1,1,21202,-2,1,3,21101,0,343,0,1106,0,303,1106,0,415,22207,-2,-3,-1,1206,-1,387,22201,-3,-2,-3,21202,-2,-1,-1,22201,-3,-1,3,21202,3,-1,-1,22201,-3,-1,2,21201,-4,0,1,21101,384,0,0,1105,1,303,1105,1,415,21202,-4,-1,-4,22201,-4,-3,-4,22202,-3,-2,-2,22202,-2,-4,-4,22202,-3,-2,-3,21202,-4,-1,-2,22201,-3,-2,1,21202,1,1,-4,109,-5,2105,1,0

main.go

@@ -51,6 +51,8 @@ var dayMap = []day{
 	&days.Day15{},
 	&days.Day16{},
 	&days.Day17{},
+	&days.Day18{},
+	&days.Day19{},
 }
 
 func main() {

utilities/bisect.go

@@ -0,0 +1,27 @@
+package utilities
+
+import (
+	"fmt"
+	"math"
+)
+
+// Bisect takes a known-good low and known-bad high value as the bounds
+// to bisect, and a function to test each value for success or failure.
+// If the function succeeds, the value is adjusted toward the maximum,
+// and if the function fails, the value is adjusted toward the minimum.
+// The final value is returned when the difference between the success
+// and the failure is less than or equal to the acceptance threshold
+// (usually 1, for integers).
+func Bisect[T Number](low, high, threshold T, tryFunc func(val T) bool) T {
+	for T(math.Abs(float64(high-low))) > threshold {
+		currVal := low + ((high - low) / 2)
+		success := tryFunc(currVal)
+		if success {
+			low = currVal
+		} else {
+			high = currVal
+		}
+	}
+
+	return low
+}

utilities/intcode.go

@@ -128,9 +128,15 @@ func (p *IntcodeProgram) ensureMemoryCapacity(address int) {
 }
 
 func (p *IntcodeProgram) Reset() {
+	wiped := false
+	if len(p.memory) != len(p.program) {
+		wiped = true
 		p.memory = nil
+	}
 	p.init()
+	if !wiped {
 		copy(p.memory, p.program)
+	}
 	p.relativeBase = 0
 }
 

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

@@ -44,11 +44,16 @@ func (v Vec2[T]) Equals(other Vec2[T]) bool {
 		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,
+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 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 {