Finished day 6

2024/day6/main.go

@@ -0,0 +1,197 @@
+package main
+
+import (
+	"bufio"
+	"flag"
+	"fmt"
+	"os"
+	"sync"
+	"time"
+)
+
+var transformations = map[Direction]func(loc Location) Location{
+	NORTH: func(loc Location) Location { return Location{X: loc.X, Y: loc.Y - 1} },
+	SOUTH: func(loc Location) Location { return Location{X: loc.X, Y: loc.Y + 1} },
+	EAST:  func(loc Location) Location { return Location{X: loc.X + 1, Y: loc.Y} },
+	WEST:  func(loc Location) Location { return Location{X: loc.X - 1, Y: loc.Y} },
+}
+
+func applyTransform(loc Location, direction Direction, grid [][]string) (Location, bool) {
+	newLoc := transformations[direction](loc)
+	if newLoc.X < 0 || newLoc.X >= len(grid[0]) || newLoc.Y < 0 || newLoc.Y >= len(grid) {
+		return loc, false
+	}
+
+	return newLoc, true
+}
+
+type Direction string
+type Location struct{ Y, X int }
+
+const (
+	NORTH Direction = "N"
+	SOUTH Direction = "S"
+	EAST  Direction = "E"
+	WEST  Direction = "W"
+)
+
+func turnRight(direction Direction) Direction {
+	switch direction {
+	case NORTH:
+		return EAST
+	case EAST:
+		return SOUTH
+	case SOUTH:
+		return WEST
+	case WEST:
+		return NORTH
+	}
+	return ""
+}
+
+func checkLoop(grid [][]string, initial, obstruction Location) bool {
+	visited := make([][][]Direction, len(grid))
+	for i := range visited {
+		visited[i] = make([][]Direction, len(grid[0]))
+	}
+
+	direction := NORTH
+	loc := initial
+	for loc.X >= 0 && loc.X < len(grid[0]) && loc.Y >= 0 && loc.Y < len(grid) {
+		for _, dir := range visited[loc.Y][loc.X] {
+			if dir == direction {
+				return true
+			}
+		}
+
+		visited[loc.Y][loc.X] = append(visited[loc.Y][loc.X], direction)
+
+		newLoc, status := applyTransform(loc, direction, grid)
+		if !status {
+			break
+		}
+
+		if grid[newLoc.Y][newLoc.X] == "#" || newLoc == obstruction {
+			newLoc = loc
+			direction = turnRight(direction)
+		}
+
+		loc = newLoc
+	}
+
+	return false
+}
+
+func Part1(grid [][]string, initial Location) int {
+	visited := make([][]bool, len(grid))
+	for i := range visited {
+		visited[i] = make([]bool, len(grid[0]))
+	}
+
+	direction := NORTH
+	loc := initial
+	for loc.X >= 0 && loc.X < len(grid[0]) && loc.Y >= 0 && loc.Y < len(grid) {
+		visited[loc.Y][loc.X] = true
+
+		newLoc := transformations[direction](loc)
+		if newLoc.X < 0 || newLoc.X >= len(grid[0]) || newLoc.Y < 0 || newLoc.Y >= len(grid) {
+			break
+		}
+
+		if grid[newLoc.Y][newLoc.X] == "#" {
+			newLoc = loc
+			direction = turnRight(direction)
+		}
+
+		loc = newLoc
+	}
+
+	visitedCount := 0
+	for row := range visited {
+		for col := range visited[row] {
+			if visited[row][col] {
+				visitedCount++
+			}
+		}
+	}
+
+	return visitedCount
+}
+
+func Part2(grid [][]string, initial Location) int {
+	var wg sync.WaitGroup
+	res := make(chan bool)
+
+	for row := range grid {
+		for col := range grid[row] {
+			wg.Add(1)
+
+			go func(row, col int) {
+				defer wg.Done()
+
+				isLoop := checkLoop(grid, initial, Location{X: col, Y: row})
+				res <- isLoop
+			}(row, col)
+		}
+	}
+
+	go func() {
+		defer close(res)
+		wg.Wait()
+	}()
+
+	total := 0
+	for result := range res {
+		if result {
+			total += 1
+		}
+	}
+
+	return total
+}
+
+func main() {
+	flag.Parse()
+
+	if len(flag.Args()) == 0 {
+		panic("Please provide a filename")
+	}
+
+	filename := flag.Args()[0]
+
+	file, err := os.Open(filename)
+	if err != nil {
+		panic(err)
+	}
+	defer file.Close()
+
+	grid := [][]string{}
+	initialLocation := Location{X: -1, Y: -1}
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		row := []string{}
+		for _, char := range line {
+			row = append(row, string(char))
+
+			if char == '^' {
+				initialLocation.Y = len(grid)
+				initialLocation.X = len(row) - 1
+			}
+		}
+
+		grid = append(grid, row)
+	}
+
+	if err := scanner.Err(); err != nil {
+		panic(err)
+	}
+
+	answer := Part1(grid, initialLocation)
+	fmt.Println(answer)
+
+	start := time.Now()
+	answer = Part2(grid, initialLocation)
+	fmt.Println(answer, time.Since(start))
+}

2024/inputs/day6.txt

@@ -0,0 +1,130 @@
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