Day 11 solution.

2020/day11.go

@@ -0,0 +1,129 @@
+package main
+
+// step 1:
+//   2129 too low
+
+import (
+	"fmt"
+	"os"
+
+	"git.annabunch.es/annabunches/adventofcode/2020/lib/fileutils"
+)
+
+func occupied1(board [][]byte, i, j int) int {
+	if i < 0 || j < 0 || i >= len(board) || j >= len(board[0]) {
+		return 0
+	}
+
+	if board[i][j] == '#' {
+		return 1
+	}
+
+	return 0
+}
+
+func occupied2(board [][]byte, i, j, iDir, jDir, level int) int {
+	si := i + (iDir * level)
+	sj := j + (jDir * level)
+
+	if si < 0 || sj < 0 || si >= len(board) || sj >= len(board[0]) {
+		return 0
+	}
+
+	if board[si][sj] == 'L' {
+		return 0
+	}
+
+	if board[si][sj] == '#' {
+		return 1
+	}
+
+	return occupied2(board, i, j, iDir, jDir, level+1)
+}
+
+func getNewValue(board [][]byte, i, j int, step string) byte {
+	if board[i][j] == '.' {
+		return '.'
+	}
+
+	occ := 0
+	occLimit := 4
+
+	switch step {
+	case "1":
+		occ = occupied1(board, i-1, j-1) +
+			occupied1(board, i-1, j) +
+			occupied1(board, i-1, j+1) +
+			occupied1(board, i, j-1) +
+			occupied1(board, i, j+1) +
+			occupied1(board, i+1, j-1) +
+			occupied1(board, i+1, j) +
+			occupied1(board, i+1, j+1)
+	case "2":
+		occLimit = 5
+		occ = occupied2(board, i, j, -1, -1, 1) +
+			occupied2(board, i, j, -1, 0, 1) +
+			occupied2(board, i, j, -1, +1, 1) +
+			occupied2(board, i, j, 0, -1, 1) +
+			occupied2(board, i, j, 0, +1, 1) +
+			occupied2(board, i, j, 1, -1, 1) +
+			occupied2(board, i, j, 1, 0, 1) +
+			occupied2(board, i, j, 1, +1, 1)
+	}
+
+	if board[i][j] == 'L' && occ == 0 {
+		return '#'
+	}
+
+	if board[i][j] == '#' && occ >= occLimit {
+		return 'L'
+	}
+
+	return board[i][j]
+}
+
+func countOccupied(board [][]byte) int {
+	count := 0
+
+	for i := 0; i < len(board); i++ {
+		for j := 0; j < len(board[0]); j++ {
+			if board[i][j] == '#' {
+				count++
+			}
+		}
+	}
+
+	return count
+}
+
+func main() {
+	step := os.Args[1]
+	board := fileutils.InputParserBytes(os.Args[2])
+
+	changed := true
+	for changed {
+		changed = false
+
+		// initialize the next generation
+		newBoard := make([][]byte, len(board))
+		for i := 0; i < len(newBoard); i++ {
+			newBoard[i] = make([]byte, len(board[0]))
+			copy(newBoard[i], board[i])
+		}
+
+		for i := 0; i < len(board); i++ {
+			for j := 0; j < len(board[0]); j++ {
+				value := getNewValue(board, i, j, step)
+
+				if board[i][j] != value {
+					newBoard[i][j] = value
+					changed = true
+				}
+			}
+		}
+
+		board = newBoard
+	}
+
+	fmt.Println(countOccupied(board))
+}

2020/lib/fileutils/fileutils.go

@@ -2,6 +2,7 @@ package fileutils
 
 import (
 	"bufio"
+	"bytes"
 	"io/ioutil"
 	"log"
 	"os"
@@ -58,3 +59,12 @@ func InputParserStrings(filename string) []string {
 	}
 	return strings.Split(string(data), "\n")
 }
+
+func InputParserBytes(filename string) [][]byte {
+	data, err := ioutil.ReadFile(filename)
+	if err != nil {
+		log.Panicf(err.Error())
+	}
+	output := bytes.Split(data, []byte("\n"))
+	return output[:len(output)-1]
+}