[2024] Solution for Day 8

Author: kfarnung

2024/day08/main.go

@@ -0,0 +1,112 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+
+	"github.com/kfarnung/advent-of-code/2024/lib"
+)
+
+type antenna struct {
+	location  point
+	frequency rune
+}
+
+type point struct {
+	x, y int
+}
+
+func part1(input string) int64 {
+	antennas, width, height := parseMap(input)
+	antinodes := make(map[point]bool)
+	for _, antenna := range antennas {
+		for _, antenna2 := range antennas {
+			if antenna.location == antenna2.location || antenna.frequency != antenna2.frequency {
+				continue
+			}
+
+			delta := point{antenna2.location.x - antenna.location.x, antenna2.location.y - antenna.location.y}
+			antinode1 := point{antenna.location.x + delta.x, antenna.location.y + delta.y}
+			antinode2 := point{antenna.location.x - delta.x, antenna.location.y - delta.y}
+			antinode3 := point{antenna2.location.x + delta.x, antenna2.location.y + delta.y}
+			antinode4 := point{antenna2.location.x - delta.x, antenna2.location.y - delta.y}
+
+			if antinode1 != antenna2.location && antinode1.x >= 0 && antinode1.x < width && antinode1.y >= 0 && antinode1.y < height {
+				antinodes[antinode1] = true
+			}
+
+			if antinode2 != antenna2.location && antinode2.x >= 0 && antinode2.x < width && antinode2.y >= 0 && antinode2.y < height {
+				antinodes[antinode2] = true
+			}
+
+			if antinode3 != antenna.location && antinode3.x >= 0 && antinode3.x < width && antinode3.y >= 0 && antinode3.y < height {
+				antinodes[antinode3] = true
+			}
+
+			if antinode4 != antenna.location && antinode4.x >= 0 && antinode4.x < width && antinode4.y >= 0 && antinode4.y < height {
+				antinodes[antinode4] = true
+			}
+		}
+	}
+
+	return int64(len(antinodes))
+}
+
+func part2(input string) int64 {
+	antennas, rows, cols := parseMap(input)
+	antinodes := make(map[point]bool)
+	for _, antenna := range antennas {
+		for _, antenna2 := range antennas {
+			if antenna.location == antenna2.location || antenna.frequency != antenna2.frequency {
+				continue
+			}
+
+			delta := point{antenna2.location.x - antenna.location.x, antenna2.location.y - antenna.location.y}
+			antinodeLocation := point{antenna.location.x + delta.x, antenna.location.y + delta.y}
+			for antinodeLocation.x >= 0 && antinodeLocation.x < rows && antinodeLocation.y >= 0 && antinodeLocation.y < cols {
+				antinodes[antinodeLocation] = true
+				antinodeLocation = point{antinodeLocation.x + delta.x, antinodeLocation.y + delta.y}
+			}
+
+			antinodeLocation = point{antenna.location.x - delta.x, antenna.location.y - delta.y}
+			for antinodeLocation.x >= 0 && antinodeLocation.x < rows && antinodeLocation.y >= 0 && antinodeLocation.y < cols {
+				antinodes[antinodeLocation] = true
+				antinodeLocation = point{antinodeLocation.x - delta.x, antinodeLocation.y - delta.y}
+			}
+		}
+	}
+
+	return int64(len(antinodes))
+}
+
+func parseMap(input string) ([]antenna, int, int) {
+	var antennas []antenna
+	rows := 0
+	lines := lib.SplitLines(input)
+	for x, line := range lines {
+		if len(line) == 0 {
+			continue
+		}
+
+		rows++
+
+		for y, frequency := range line {
+			if frequency != '.' {
+				antennas = append(antennas, antenna{point{x, y}, frequency})
+			}
+		}
+	}
+	return antennas, rows, len(lines[0])
+}
+
+func main() {
+	name := os.Args[1]
+	content, err := lib.LoadFileContent(name)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Printf("Part 1: %d\n", part1(content))
+	fmt.Printf("Part 2: %d\n", part2(content))
+}

2024/day08/main_test.go

@@ -0,0 +1,47 @@
+package main
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/kfarnung/advent-of-code/2024/lib"
+	"github.com/stretchr/testify/assert"
+)
+
+var input = strings.Join([]string{
+	"............",
+	"........0...",
+	".....0......",
+	".......0....",
+	"....0.......",
+	"......A.....",
+	"............",
+	"............",
+	"........A...",
+	".........A..",
+	"............",
+	"............",
+	"",
+}, "\n")
+
+func TestPart1(t *testing.T) {
+	assert.Equal(t, int64(14), part1(input))
+
+	inputContent, err := lib.GetInputContent()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, int64(327), part1(inputContent))
+}
+
+func TestPart2(t *testing.T) {
+	assert.Equal(t, int64(34), part2(input))
+
+	inputContent, err := lib.GetInputContent()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, int64(1233), part2(inputContent))
+}