day8: solved puzzle 1

Author: fxnn

day8/example.txt

@@ -0,0 +1,12 @@
+............
+........0...
+.....0......
+.......0....
+....0.......
+......A.....
+............
+............
+........A...
+.........A..
+............
+............

day8/main.go

@@ -0,0 +1,71 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"regexp"
+
+	"github.com/fxnn/adventofcode2024/util"
+)
+
+const ANTENNA_PATTERN = "[a-zA-Z0-9]"
+
+func discoverAntennaPoints(lines [][]byte) map[byte][]util.Point {
+	var antennaPattern = regexp.MustCompile(ANTENNA_PATTERN)
+	var antennaPoints = make(map[byte][]util.Point)
+	for y, line := range lines {
+		for x, b := range line {
+			if antennaPattern.Match([]byte{b}) {
+				var list []util.Point
+				if l, ok := antennaPoints[b]; ok {
+					list = l
+				} else {
+					list = make([]util.Point, 0)
+				}
+				antennaPoints[b] = append(list, util.Point{Y: y, X: x})
+			}
+		}
+	}
+	return antennaPoints
+}
+
+func discoverAntinodes(antennaPoints map[byte][]util.Point, mapHeight int, mapWidth int) map[util.Point]util.Void {
+	var antinodes = make(map[util.Point]util.Void)
+	for _, points := range antennaPoints {
+		for i, point := range points {
+			for j, otherPoint := range points {
+				if i == j {
+					continue
+				}
+				var delta = point.Subtract(otherPoint)
+				var antinode1 = point.Add(delta)
+				if antinode1.IsInBounds(mapHeight, mapWidth) {
+					antinodes[antinode1] = util.Void{}
+				}
+				var antinode2 = otherPoint.Subtract(delta)
+				if antinode2.IsInBounds(mapHeight, mapWidth) {
+					antinodes[antinode2] = util.Void{}
+				}
+			}
+		}
+	}
+	return antinodes
+}
+
+func main() {
+	scanner := bufio.NewScanner(os.Stdin)
+	scanner.Split(bufio.ScanLines)
+
+	var lines [][]byte
+	for scanner.Scan() {
+		lines = append(lines, scanner.Bytes())
+	}
+
+	var mapHeight = len(lines)
+	var mapWidth = len(lines[0])
+	var antennaPoints = discoverAntennaPoints(lines)
+	var antinodes = discoverAntinodes(antennaPoints, mapHeight, mapWidth)
+
+	fmt.Printf("unique antinodes: %d\n", len(antinodes))
+}

util/point.go

@@ -0,0 +1,37 @@
+package util
+
+type Point struct {
+	Y int
+	X int
+}
+
+func (p *Point) Add(o Point) Point {
+	return Point{Y: p.Y + o.Y, X: p.X + o.X}
+}
+
+func (p *Point) Subtract(o Point) Point {
+	return Point{Y: p.Y - o.Y, X: p.X - o.X}
+}
+
+func (p *Point) IsInBounds(height, width int) bool {
+	if p.Y < 0 || p.Y >= height {
+		return false
+	}
+	if p.X < 0 || p.X >= width {
+		return false
+	}
+	return true
+}
+
+func ByteAt(lines [][]byte, p Point) (byte, bool) {
+	if p.Y < 0 || p.X < 0 {
+		return 0, false
+	}
+	if p.Y >= len(lines) {
+		return 0, false
+	}
+	if p.X >= len(lines[p.Y]) {
+		return 0, false
+	}
+	return lines[p.Y][p.X], true
+}

util/util.go

@@ -6,6 +6,8 @@ import (
 	"strconv"
 )
 
+type Void struct{}
+
 // Atoi converts string to integer, and exist immediately upon error
 func Atoi(s string) int {
 	if i, err := strconv.Atoi(s); err != nil {