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/24.go

@@ -51,6 +51,96 @@ func (d Day24) calcActivatedNeighbors(grid [][]bool, i, j int) int {
 	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 {
@@ -65,6 +155,20 @@ func (d Day24) calcRating(grid [][]bool) int {
 	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)
@@ -113,7 +217,7 @@ func (d *Day24) Part1() string {
 		rating := d.calcRating(scratch)
 		if u.ArrayContains(seenRatings, rating) {
 			found = true
-			d.Draw(scratch)
+			// d.Draw(scratch)
 			answer = rating
 		}
 		seenRatings = append(seenRatings, rating)
@@ -124,5 +228,62 @@ func (d *Day24) Part1() string {
 }
 
 func (d *Day24) Part2() string {
-	return fmt.Sprintf("%s%d%s", u.TextBold, 0, u.TextReset)
+	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)
 }