Solution for 2024, day 18

Author: lucianoq

2024/18/Makefile

@@ -0,0 +1,19 @@
+input:
+	http "https://adventofcode.com/2024/day/18/input" "Cookie:session=${AOC_SESSION};" >input
+
+main1:
+	go build -o main1 main1.go common.go
+
+main2:
+	go build -o main2 main2.go common.go
+
+.PHONY: run1 run2 clean
+
+run1: main1 input
+	./main1 <input
+
+run2: main2 input
+	./main2 <input
+
+clean:
+	rm -f main1 main2 input

2024/18/common.go

@@ -0,0 +1,69 @@
+package main
+
+import (
+	"bufio"
+	"os"
+	"strconv"
+	"strings"
+)
+
+const Size = 70
+
+type P struct{ x, y int }
+
+var (
+	Start = P{0, 0}
+	Goal  = P{Size, Size}
+	Delta = []P{{0, 1}, {1, 0}, {0, -1}, {-1, 0}}
+)
+
+func parseInput() []P {
+	var m []P
+	scanner := bufio.NewScanner(os.Stdin)
+	for i := 0; scanner.Scan(); i++ {
+		ff := strings.Split(scanner.Text(), ",")
+		x, _ := strconv.Atoi(ff[0])
+		y, _ := strconv.Atoi(ff[1])
+		m = append(m, P{x, y})
+	}
+	return m
+}
+
+func BFS(corrupted map[P]struct{}) []P {
+	queue := []P{Start}
+	visited := map[P]struct{}{Start: {}}
+	parent := map[P]P{}
+
+	for len(queue) > 0 {
+		var curr P
+		curr, queue = queue[0], queue[1:]
+
+		if curr == Goal {
+			var path []P
+			for p := Goal; p != Start; p = parent[p] {
+				path = append(path, p)
+			}
+			return path
+		}
+
+		for _, d := range Delta {
+			n := P{curr.x + d.x, curr.y + d.y}
+
+			if n.x < 0 || n.x > Size || n.y < 0 || n.y > Size {
+				continue
+			}
+
+			if _, ok := corrupted[n]; ok {
+				continue
+			}
+
+			if _, ok := visited[n]; !ok {
+				visited[n] = struct{}{}
+				parent[n] = curr
+				queue = append(queue, n)
+			}
+		}
+	}
+
+	return nil
+}

2024/18/main1.go

@@ -0,0 +1,14 @@
+package main
+
+import "fmt"
+
+func main() {
+	bytes := parseInput()
+
+	corrupted := map[P]struct{}{}
+	for _, p := range bytes[:1024] {
+		corrupted[p] = struct{}{}
+	}
+
+	fmt.Println(len(BFS(corrupted)))
+}

2024/18/main2.go

@@ -0,0 +1,16 @@
+package main
+
+import "fmt"
+
+func main() {
+	bytes := parseInput()
+
+	corrupted := map[P]struct{}{}
+	for _, p := range bytes {
+		corrupted[p] = struct{}{}
+		if path := BFS(corrupted); path == nil {
+			fmt.Printf("%d,%d\n", p.x, p.y)
+			return
+		}
+	}
+}