Solution for 2024, day 8

Author: lucianoq

2024/8/Makefile

@@ -0,0 +1,19 @@
+input:
+	http "https://adventofcode.com/2024/day/8/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

2024/8/common.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"bufio"
+	"os"
+)
+
+const Size = 50
+
+type P struct {
+	X, Y int
+}
+
+func (p P) Valid() bool {
+	return p.X >= 0 && p.X < Size && p.Y >= 0 && p.Y < Size
+}
+
+func parseInput() map[byte][]P {
+	scanner := bufio.NewScanner(os.Stdin)
+
+	freqs := map[byte][]P{}
+	for i := 0; scanner.Scan(); i++ {
+		line := scanner.Text()
+
+		for j, c := range line {
+			if c == '.' {
+				continue
+			}
+
+			ch := byte(c)
+
+			freqs[ch] = append(freqs[ch], P{i, j})
+		}
+	}
+
+	return freqs
+}

2024/8/main1.go

@@ -0,0 +1,28 @@
+package main
+
+import "fmt"
+
+func main() {
+	freqs := parseInput()
+
+	antiNodes := map[P]struct{}{}
+	for _, locs := range freqs {
+		for a := 0; a < len(locs)-1; a++ {
+			for b := a + 1; b < len(locs); b++ {
+				delta := P{locs[b].X - locs[a].X, locs[b].Y - locs[a].Y}
+
+				anti1 := P{locs[a].X - delta.X, locs[a].Y - delta.Y}
+				if anti1.X >= 0 && anti1.X < Size && anti1.Y >= 0 && anti1.Y < Size {
+					antiNodes[anti1] = struct{}{}
+				}
+
+				anti2 := P{locs[b].X + delta.X, locs[b].Y + delta.Y}
+				if anti2.X >= 0 && anti2.X < Size && anti2.Y >= 0 && anti2.Y < Size {
+					antiNodes[anti2] = struct{}{}
+				}
+			}
+		}
+	}
+
+	fmt.Println(len(antiNodes))
+}

2024/8/main2.go

@@ -0,0 +1,37 @@
+package main
+
+import "fmt"
+
+func main() {
+	freqs := parseInput()
+
+	antiNodes := map[P]struct{}{}
+	for _, locs := range freqs {
+		for a := 0; a < len(locs)-1; a++ {
+			for b := a + 1; b < len(locs); b++ {
+				delta := P{locs[b].X - locs[a].X, locs[b].Y - locs[a].Y}
+
+				outOfBound := 0
+				for period := 0; outOfBound < 2; period++ {
+					outOfBound = 0
+
+					anti1 := P{locs[a].X - period*delta.X, locs[a].Y - period*delta.Y}
+					if anti1.Valid() {
+						antiNodes[anti1] = struct{}{}
+					} else {
+						outOfBound++
+					}
+
+					anti2 := P{locs[b].X + period*delta.X, locs[b].Y + period*delta.Y}
+					if anti2.Valid() {
+						antiNodes[anti2] = struct{}{}
+					} else {
+						outOfBound++
+					}
+				}
+			}
+		}
+	}
+
+	fmt.Println(len(antiNodes))
+}