Update: 2024 Day 18

Author: suhasksv

2024/day-18/main.go

@@ -0,0 +1,144 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type Point struct {
+	X, Y int
+}
+
+func parseInput(fileName string) ([]Point, error) {
+	file, err := os.Open(fileName)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+
+	var points []Point
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		line := scanner.Text()
+		coords := strings.Split(line, ",")
+		if len(coords) != 2 {
+			return nil, fmt.Errorf("invalid input format: %s", line)
+		}
+		x, err1 := strconv.Atoi(coords[0])
+		y, err2 := strconv.Atoi(coords[1])
+		if err1 != nil || err2 != nil {
+			return nil, fmt.Errorf("invalid coordinates: %s", line)
+		}
+		points = append(points, Point{X: x, Y: y})
+	}
+	return points, nil
+}
+
+func buildGrid(size int) [][]bool {
+	grid := make([][]bool, size)
+	for i := range grid {
+		grid[i] = make([]bool, size)
+	}
+	return grid
+}
+
+func bfs(grid [][]bool, start, end Point) bool {
+	size := len(grid)
+	directions := []Point{{0, 1}, {1, 0}, {0, -1}, {-1, 0}}
+	queue := []Point{start}
+	visited := make(map[Point]bool)
+	visited[start] = true
+
+	for len(queue) > 0 {
+		curr := queue[0]
+		queue = queue[1:]
+
+		if curr == end {
+			return true
+		}
+
+		for _, dir := range directions {
+			next := Point{X: curr.X + dir.X, Y: curr.Y + dir.Y}
+			if next.X >= 0 && next.X < size && next.Y >= 0 && next.Y < size && !grid[next.Y][next.X] && !visited[next] {
+				visited[next] = true
+				queue = append(queue, next)
+			}
+		}
+	}
+
+	return false
+}
+
+func findShortestPath(grid [][]bool, start, end Point) int {
+	size := len(grid)
+	directions := []Point{{0, 1}, {1, 0}, {0, -1}, {-1, 0}}
+	queue := []struct {
+		Point Point
+		Steps int
+	}{{Point: start, Steps: 0}}
+	visited := make(map[Point]bool)
+	visited[start] = true
+
+	for len(queue) > 0 {
+		curr := queue[0]
+		queue = queue[1:]
+
+		if curr.Point == end {
+			return curr.Steps
+		}
+
+		for _, dir := range directions {
+			next := Point{X: curr.Point.X + dir.X, Y: curr.Point.Y + dir.Y}
+			if next.X >= 0 && next.X < size && next.Y >= 0 && next.Y < size && !grid[next.Y][next.X] && !visited[next] {
+				visited[next] = true
+				queue = append(queue, struct {
+					Point Point
+					Steps int
+				}{Point: next, Steps: curr.Steps + 1})
+			}
+		}
+	}
+
+	return -1
+}
+
+func main() {
+	inputFile := "input.txt"
+	points, err := parseInput(inputFile)
+	if err != nil {
+		fmt.Println("Error parsing input:", err)
+		return
+	}
+
+	size := 71
+	grid := buildGrid(size)
+	start := Point{X: 0, Y: 0}
+	end := Point{X: size - 1, Y: size - 1}
+
+	// Part 1: Find the shortest path after 1024 bytes
+	for i := 0; i < 1024 && i < len(points); i++ {
+		point := points[i]
+		grid[point.Y][point.X] = true
+	}
+	shortestPath := findShortestPath(grid, start, end)
+	if shortestPath == -1 {
+		fmt.Println("No valid path to the exit after 1024 bytes.")
+	} else {
+		fmt.Printf("Shortest Path after 1024 bytes: %d\n", shortestPath)
+	}
+
+	// Reset the grid for Part 2
+	grid = buildGrid(size)
+
+	// Part 2: Find the first byte that blocks the path
+	for _, point := range points {
+		grid[point.Y][point.X] = true
+		if !bfs(grid, start, end) {
+			fmt.Printf("First blocking byte: %d,%d\n", point.X, point.Y)
+			break
+		}
+	}
+}