Finished day 8

2024/day8/main.go

@@ -0,0 +1,121 @@
+package main
+
+import (
+	"bufio"
+	"flag"
+	"fmt"
+	"os"
+)
+
+type Point struct {
+	x, y int
+}
+
+func isValid(p Point, rows, cols int) bool {
+	return p.x >= 0 && p.x < rows && p.y >= 0 && p.y < cols
+}
+
+func Part1(grid map[rune][]Point, rows, cols int) int {
+	antinodes := make(map[Point]bool)
+
+	for _, antennas := range grid {
+		if len(antennas) < 2 {
+			continue
+		}
+
+		for i := 0; i < len(antennas); i++ {
+			for j := i + 1; j < len(antennas); j++ {
+				a1, a2 := antennas[i], antennas[j]
+				dx, dy := a2.x-a1.x, a2.y-a1.y
+
+				forward := Point{a1.x - dx, a1.y - dy}
+				if isValid(forward, rows, cols) {
+					antinodes[forward] = true
+				}
+
+				backward := Point{a2.x + dx, a2.y + dy}
+				if isValid(backward, rows, cols) {
+					antinodes[backward] = true
+				}
+			}
+		}
+	}
+
+	return len(antinodes)
+}
+
+func Part2(grid map[rune][]Point, rows, cols int) int {
+	antinodes := make(map[Point]bool)
+	for _, antennas := range grid {
+		if len(antennas) < 2 {
+			continue
+		}
+
+		for i := 0; i < len(antennas); i++ {
+			for j := i + 1; j < len(antennas); j++ {
+				a1, a2 := antennas[i], antennas[j]
+
+				antinodes[a1] = true
+				antinodes[a2] = true
+
+				dx, dy := a2.x-a1.x, a2.y-a1.y
+
+				forward := Point{a1.x - dx, a1.y - dy}
+				for isValid(forward, rows, cols) {
+					antinodes[forward] = true
+					forward = Point{forward.x - dx, forward.y - dy}
+				}
+
+				backward := Point{a2.x + dx, a2.y + dy}
+				for isValid(backward, rows, cols) {
+					antinodes[backward] = true
+					backward = Point{backward.x + dx, backward.y + dy}
+				}
+			}
+		}
+	}
+
+	return len(antinodes)
+}
+
+func main() {
+	flag.Parse()
+
+	if len(flag.Args()) == 0 {
+		panic("Please provide a filename")
+	}
+
+	filename := flag.Args()[0]
+
+	file, err := os.Open(filename)
+	if err != nil {
+		panic(err)
+	}
+	defer file.Close()
+
+	grid := make(map[rune][]Point)
+	scanner := bufio.NewScanner(file)
+	rows, cols := 0, 0
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		for c, ch := range line {
+			if ch != '.' {
+				grid[ch] = append(grid[ch], Point{rows, c})
+			}
+		}
+
+		cols = len(line)
+		rows++
+	}
+
+	if err := scanner.Err(); err != nil {
+		panic(err)
+	}
+
+	answer := Part1(grid, rows, cols)
+	fmt.Println(answer)
+
+	answer = Part2(grid, rows, cols)
+	fmt.Println(answer)
+}

2024/inputs/day8.txt

@@ -0,0 +1,50 @@
+.....wV....q.....................................n
+.......w......q.h.....Vn.........................D
+............w.S..G.....................DT.........
+......S........h......e..T.....y......D...........
+......m.......Ae.......T........o.................
+....m....S........................................
+...m..........................n........8..........
+.........2...G......................n.............
+..2........V.......h................Q.............
+............................o.....................
+.Z......I..U....e...u.....G....o..................
+...N..G.........................................y.
+.....I............q.......h...................s...
+......U........qI....o.V..Rz........8........k....
+......d.Z.........................R.......8y......
+.........e..............T.....l...................
+.......2.........................u...R............
+.....d.............................Q..............
+...................v.....................s.Q....M.
+........2..........4.....................8..7.k...
+...........x..N..................A..........k.....
+...........ZN...........v...............K.........
+...d.......N.....................Ky.6.............
+...........................l6.....................
+....L....g.................4.......k..K.......0...
+..............L...........4R................s.....
+U......r..............H.4.........................
+.......U.............a.......H.............u......
+......xY...............l..........................
+...................................6..u...........
+........Y......L......l............0..............
+......9..L...........A.....v..HEa........K........
+..................v........6.EX.............z.....
+d..Y.............m......A.........................
+......................a.i......M...........z......
+...................g.......................0......
+...............................H.........i........
+..........3................W........E...i...0.....
+.................t.a....g.................5.......
+.r...t...........................7.....5..........
+....................................7....5........
+....................g.Y...wMz.....................
+9..........O....3................W.7..E..XD...1...
+t..............3.x.....9..........W.M.............
+...9............W.................................
+Z.............x................X.i......5.........
+...........3.....................................1
+...................O.......s....X.................
+..............r...................................
+..........................O.................1.....