day 08 solution

solutions/alessio/day08/day08.go

@@ -0,0 +1,112 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+func check(e error) {
+	if e != nil {
+		panic(e)
+	}
+}
+
+type Cell struct {
+	r, c int
+}
+
+func checkInBounds(cell Cell, rows int, cols int) bool {
+	return cell.r >= 0 && cell.r < rows && cell.c >= 0 && cell.c < cols
+}
+
+func part1(lines []string) {
+	rows, cols := len(lines), len(lines[0])
+	antennas := make(map[byte][]Cell)
+	for r := range rows {
+		for c := range cols {
+			if lines[r][c] != '.' {
+				antennas[lines[r][c]] = append(antennas[lines[r][c]], Cell{r, c})
+			}
+		}
+	}
+
+	antinodes := make(map[Cell]bool)
+	for _, places := range antennas {
+		for i := range len(places) {
+			for j := i + 1; j < len(places); j++ {
+				p1, p2 := places[i], places[j]
+				dr, dc := p2.r-p1.r, p2.c-p1.c
+				antinode1 := Cell{p2.r + dr, p2.c + dc}
+				if checkInBounds(antinode1, rows, cols) {
+					antinodes[antinode1] = true
+				}
+				antinode2 := Cell{p1.r - dr, p1.c - dc}
+				if checkInBounds(antinode2, rows, cols) {
+					antinodes[antinode2] = true
+				}
+			}
+		}
+	}
+
+	fmt.Println(len(antinodes))
+}
+
+func part2(lines []string) {
+	rows, cols := len(lines), len(lines[0])
+	antennas := make(map[byte][]Cell)
+	for r := range rows {
+		for c := range cols {
+			if lines[r][c] != '.' {
+				antennas[lines[r][c]] = append(antennas[lines[r][c]], Cell{r, c})
+			}
+		}
+	}
+
+	antinodes := make(map[Cell]bool)
+	for _, places := range antennas {
+		for i := range len(places) {
+			for j := i + 1; j < len(places); j++ {
+				p1, p2 := places[i], places[j]
+				// mark also antennas as antinodes
+				antinodes[p1] = true
+				antinodes[p2] = true
+
+				dr, dc := p2.r-p1.r, p2.c-p1.c
+				cnt := 1
+				for {
+					antinode := Cell{p2.r + cnt*dr, p2.c + cnt*dc}
+					if checkInBounds(antinode, rows, cols) {
+						antinodes[antinode] = true
+						cnt++
+					} else {
+						break
+					}
+				}
+
+				cnt = 1
+				for {
+					antinode := Cell{p1.r - cnt*dr, p1.c - cnt*dc}
+					if checkInBounds(antinode, rows, cols) {
+						antinodes[antinode] = true
+						cnt++
+					} else {
+						break
+					}
+				}
+			}
+		}
+	}
+
+	fmt.Println(len(antinodes))
+}
+
+func main() {
+	data, err := os.ReadFile("./input08.txt")
+	check(err)
+
+	lines := strings.Split(strings.Trim(string(data), "\n"), "\n")
+
+	part1(lines)
+	part2(lines)
+}

solutions/alessio/day08/go.mod

@@ -0,0 +1,3 @@
+module aoc8
+
+go 1.23.3

solutions/alessio/day08/input08.txt

@@ -0,0 +1,50 @@
+.AU..Z.....8.......................t..C.6.........
+..................................................
+.....K.U....................v.....................
+...Z..A.............................v8.....t......
+p..................a8...........b...t.............
+..pU.....A..4.....................................
+..........................E.......................
+...........K..V..............v8.....Cb............
+....V................b...p........................
+....7.............................................
+....4.....A..........V......K..E.....6............
+.4.........................Vb...........0..C......
+..................................k........N......
+K....7...........9...........6.....kE.............
+......7......1...................k.......C........
+...p....................9....0.....N6.............
+..........Z........e..1...........................
+.............................E................N...
+...4...............................v0..........z..
+........U.....Z......1................z..a........
+.....5.......7......................N.............
+....................n.............................
+.......................0.9...c..........z.d.T.....
+...................n.W......a...t......D....d.....
+..........I.....e......................o9.........
+....5..2................e...........D.............
+...........................n......D...............
+......25I...1..................c......W.......o...
+................n..............D..................
+...........I........i..e..........................
+......5......2.....P..............a...............
+...........................z..................T...
+..........j.....................Wd...........O..o.
+................................................c.
+.................I................B...............
+...........u.............................T.d......
+.............................................J....
+.....3.i....u......................o..............
+3...i.............................................
+..................................................
+...........j...............W....O............w....
+...P........................J.....................
+.....u............................................
+.............................w....................
+......u.................2...w...J.................
+.....j.....B3......................O..............
+P....B..............................c.............
+................B.............w...................
+.....i.............3..............................
+..P.j....................J..........O.............