2020 day11 - 2D grid & frequency/game of life - 650/300

2020/day11/main.go

@@ -16,36 +16,152 @@ func main() {
 
 	if part == 1 {
 		ans := part1(util.ReadFile("./input.txt"))
-		util.CopyToClipboard(fmt.Sprintf("%v", ans))
 		fmt.Println("Output:", ans)
 	} else {
 		ans := part2(util.ReadFile("./input.txt"))
-		util.CopyToClipboard(fmt.Sprintf("%v", ans))
 		fmt.Println("Output:", ans)
 	}
 }
 
 func part1(input string) int {
-	parsed := parseInput(input)
-	_ = parsed
+	grid := parseInput(input)
 
-	return 0
-}
+	var lastState string
+	for {
+		grid = step(grid, 4, true)
 
-func part2(input string) int {
-	parsed := parseInput(input)
-	_ = parsed
+		// check if last grid matches current, break out if they match
+		str := stringify(grid)
+		if str == lastState {
+			break
+		}
+		lastState = str
+	}
 
-	return 0
-}
-
-func parseInput(input string) []int {
-	var ans []int
-
-	lines := strings.Split(input, "\n")
-	for _, l := range lines {
-		ans = append(ans, mathutil.StrToInt(l))
+	var ans int
+	for _, row := range grid {
+		for _, v := range row {
+			if v == "#" {
+				ans++
+			}
+		}
 	}
 
 	return ans
 }
+
+func part2(input string) int {
+	grid := parseInput(input)
+
+	var lastState string
+	for {
+		grid = step(grid, 5, false)
+
+		// check if last grid matches current, break out if they match
+		str := stringify(grid)
+		if str == lastState {
+			break
+		}
+		lastState = str
+	}
+
+	var ans int
+	for _, row := range grid {
+		for _, v := range row {
+			if v == "#" {
+				ans++
+			}
+		}
+	}
+
+	return ans
+}
+
+func parseInput(input string) [][]string {
+	var ans [][]string
+
+	lines := strings.Split(input, "\n")
+	for _, l := range lines {
+		ans = append(ans, strings.Split(l, ""))
+	}
+
+	return ans
+}
+
+// justNeighbors differentiates part 1 (true) from part 2
+// tolerance = 4 for part 1, 5 for part 2
+func step(grid [][]string, tolerance int, justNeighbors bool) [][]string {
+	var nextGrid [][]string
+
+	for r, row := range grid {
+		nextGrid = append(nextGrid, make([]string, len(grid[0])))
+		for c, v := range row {
+			if v == "." {
+				nextGrid[r][c] = "."
+			} else {
+				neighbors := countNeighbors(grid, r, c, justNeighbors)
+				// check if seats should be updated
+				if v == "L" && neighbors == 0 {
+					nextGrid[r][c] = "#"
+				} else if v == "#" && neighbors >= tolerance {
+					nextGrid[r][c] = "L"
+				} else {
+					nextGrid[r][c] = v
+				}
+			}
+		}
+
+	}
+	return nextGrid
+}
+
+var directions = [8][2]int{
+	{-1, -1},
+	{-1, 0},
+	{-1, 1},
+	{0, -1},
+	{0, 1},
+	{1, -1},
+	{1, 0},
+	{1, 1},
+}
+
+func countNeighbors(grid [][]string, row, col int, justNeighbors bool) int {
+	var countNeighbors int
+	for _, d := range directions {
+		nextR, nextC := row, col
+		for {
+			nextR += d[0]
+			nextC += d[1]
+			if nextR < 0 || nextR >= len(grid) || nextC < 0 || nextC >= len(grid[0]) {
+				break
+			}
+			if grid[nextR][nextC] == "L" {
+				break
+			}
+			if grid[nextR][nextC] == "#" {
+				countNeighbors++
+				break
+			}
+
+			// break out after first pass if only checking immediate neighbors (part 1)
+			if justNeighbors {
+				break
+			}
+		}
+	}
+
+	return countNeighbors
+}
+
+// stringifies grid so it can be compared to its former state
+func stringify(grid [][]string) string {
+	var str string
+	for _, row := range grid {
+		for _, v := range row {
+
+			str += v
+		}
+	}
+	return str
+}