might be making a mistake starting 2018...

2019/day24/part1/main.go

@@ -0,0 +1,98 @@
+package main
+
+import (
+	"adventofcode/util"
+	"fmt"
+	"strings"
+)
+
+func main() {
+	input := util.ReadFile("../input.txt")
+
+	lines := strings.Split(input, "\n")
+
+	grid := make([][]string, len(lines))
+	for i, v := range lines {
+		grid[i] = strings.Split(v, "")
+	}
+
+	// can map biodiversity scores because they're essentially bitmaps
+	previousBiodiversities := map[int]bool{getBiodiversity(grid): true}
+
+	// run indefinitely
+	for {
+		// step through a minute
+		grid = stepMinute(grid)
+		newBiodiversity := getBiodiversity(grid)
+
+		// if new biodiversity score is already in the map, print it and exit
+		if previousBiodiversities[newBiodiversity] {
+			fmt.Println("Repeated biodiversity score", newBiodiversity)
+			return
+		}
+
+		// set biodiversity score into in map
+		previousBiodiversities[newBiodiversity] = true
+	}
+}
+
+// steps through one minute and returns the next grid
+func stepMinute(grid [][]string) [][]string {
+	result := make([][]string, len(grid))
+
+	dRow := [4]int{0, 0, -1, 1}
+	dCol := [4]int{-1, 1, 0, 0}
+
+	for row, rowSli := range grid {
+		// initialize the rows for the result slice
+		result[row] = make([]string, len(grid[0]))
+
+		for col, val := range rowSli {
+			// count up the neighbors that are bugs
+			var countNeighborBugs int
+			for i := 0; i < 4; i++ {
+				nextRow, nextCol := row+dRow[i], col+dCol[i]
+				isInbounds := nextRow >= 0 && nextCol >= 0 && nextRow < len(grid) && nextCol < len(grid[0])
+				if isInbounds && grid[nextRow][nextCol] == "#" {
+					countNeighborBugs++
+				}
+			}
+
+			// determine future state of cell
+			switch val {
+			case "#":
+				// if bug has ONE neighbor only, it lives, otherwise becomes empty
+				if countNeighborBugs == 1 {
+					result[row][col] = "#"
+				} else {
+					result[row][col] = "."
+				}
+			case ".":
+				// if empty, becomes a bug if has ONE or TWO neighbors only
+				if countNeighborBugs == 1 || countNeighborBugs == 2 {
+					result[row][col] = "#"
+				} else {
+					result[row][col] = "."
+				}
+			}
+		}
+	}
+
+	return result
+}
+
+func getBiodiversity(grid [][]string) int {
+	var biodiversity int
+	for i, row := range grid {
+		for j, val := range row {
+			// dumb cheeky way to get power of two... 1 is 2^0, then shift the power
+			// 1 << 0 == 2^0 == 1; 1 << 1 == 2^1
+			powerOfTwo := 1 << (5*i + j)
+			if val == "#" {
+				biodiversity += powerOfTwo
+			}
+		}
+	}
+
+	return biodiversity
+}