Solve 2024 day 8 in go

2024/go/day-08/go.mod

@@ -0,0 +1,3 @@
+module day-08
+
+go 1.23

2024/go/day-08/input

@@ -0,0 +1,50 @@
+........................E...j......W..........L...
+............................O........E.........L..
+..q......O...........l....................K.......
+............q...................HM......W.........
+................................1..H...........IW.
+....................5.............................
+..........k........M...wl............6............
+.....O.......w...k.....5.8..l......K.........o.6..
+.......k....w.........5.........R.....o........K..
+.....q..X..............j........E...I.........K...
+............O..........E........................H.
+................Mn.h2.w.p....................H....
+..................p.......a............j.....L....
+.....X...l.p.....................m.........W..6...
+..Xq................A..................R..m.......
+.........................i..........a..........R..
+...........u.....................a........I.....2.
+k..............A..n.........R.................o...
+................n.................Qo..............
+..........u.A.........h........2..................
+...5.......Y.....p...............iN...............
+1...x.....................i.......................
+........M..............2.....Qi...................
+...............................I..e...............
+......u......A...........m..........h.............
+.......1...........U.............Qm.......j.......
+.......X.......................................9..
+.....u........U.......Y...........................
+.............................h.e..................
+..................4....e......Q.....L....N........
+.1..................4.......................y8....
+.........Y................................8.N.....
+............P.0J...........3..........8y..........
+....V3P..........J................................
+............U..P...7x...........e.................
+....................J...............r...9.........
+.........0.V......Y...............................
+...............V.4................................
+..........V..........................n............
+..............v........7..........................
+...........U..........J.......7...................
+.....v........7..........................a........
+.......................................r..........
+...........0.......x................y.............
+............6..v.x.....................N..........
+...........P......................................
+........3.......................r......4..........
+..............3......................y............
+................................................9.
+.................................................9

2024/go/day-08/main.go

@@ -0,0 +1,133 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"strings"
+)
+
+type position struct {
+	row, col int
+}
+
+func readInput() (antennas map[rune][]position, dimensions position, err error) {
+	content, err := os.ReadFile("input")
+	if err != nil {
+		return
+	}
+
+	lines := strings.Split(strings.TrimSpace(string(content)), "\n")
+	antennas = make(map[rune][]position)
+
+	for rowIndex, line := range lines {
+		for colIndex, frequency := range line {
+			if frequency != '.' {
+				antennas[frequency] = append(antennas[frequency], position{row: rowIndex, col: colIndex})
+			}
+		}
+	}
+
+	dimensions = position{row: len(lines), col: len(lines[0])}
+
+	return
+}
+
+func isInBounds(antinode, dimensions position) bool {
+	return (antinode.row >= 0 && antinode.row < dimensions.row) && (antinode.col >= 0 && antinode.col < dimensions.col)
+}
+
+func deltaVector(antenna1, antenna2 position) position {
+	return position{
+		row: antenna2.row - antenna1.row,
+		col: antenna2.col - antenna1.col,
+	}
+}
+
+func antennaPairAntinodes(antenna1, antenna2, dimensions position) []position {
+	deltaVector := deltaVector(antenna1, antenna2)
+
+	antinode1 := position{
+		row: antenna1.row - deltaVector.row,
+		col: antenna1.col - deltaVector.col,
+	}
+	antinode2 := position{
+		row: antenna2.row + deltaVector.row,
+		col: antenna2.col + deltaVector.col,
+	}
+
+	var antinodes []position
+	if isInBounds(antinode1, dimensions) {
+		antinodes = append(antinodes, antinode1)
+	}
+	if isInBounds(antinode2, dimensions) {
+		antinodes = append(antinodes, antinode2)
+	}
+
+	return antinodes
+}
+
+func antennaPairResonantAntinodes(antenna1, antenna2, dimensions position) []position {
+	var resonantAntinodes []position
+	deltaVector := deltaVector(antenna1, antenna2)
+
+	// Resonant antinodes
+	antinode1 := antenna1
+	for isInBounds(antinode1, dimensions) {
+		resonantAntinodes = append(resonantAntinodes, antinode1)
+
+		antinode1.row -= deltaVector.row
+		antinode1.col -= deltaVector.col
+	}
+
+	antinode2 := antenna2
+	for isInBounds(antinode2, dimensions) {
+		resonantAntinodes = append(resonantAntinodes, antinode2)
+
+		antinode2.row += deltaVector.row
+		antinode2.col += deltaVector.col
+	}
+
+	return resonantAntinodes
+}
+
+func findAllAntinodes(antennas map[rune][]position, dimensions position) (uniqueAntinodes, uniqueResonantAntinodes map[position]struct{}) {
+	uniqueAntinodes = make(map[position]struct{})
+	uniqueResonantAntinodes = make(map[position]struct{})
+
+	for _, frequencyGroup := range antennas {
+		for antenna1Index := 0; antenna1Index < len(frequencyGroup)-1; antenna1Index++ {
+			for antenna2Index := antenna1Index + 1; antenna2Index < len(frequencyGroup); antenna2Index++ {
+				antenna1 := frequencyGroup[antenna1Index]
+				antenna2 := frequencyGroup[antenna2Index]
+
+				foundAntinodes := antennaPairAntinodes(antenna1, antenna2, dimensions)
+				foundResonantAntinodes := antennaPairResonantAntinodes(antenna1, antenna2, dimensions)
+
+				for _, antinode := range foundAntinodes {
+					uniqueAntinodes[antinode] = struct{}{}
+				}
+
+				for _, antinode := range foundResonantAntinodes {
+					uniqueResonantAntinodes[antinode] = struct{}{}
+				}
+			}
+		}
+	}
+
+	return
+}
+
+func main() {
+	antennas, dimensions, err := readInput()
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	uniqueAntinodes, uniqueResonantAntinodes := findAllAntinodes(antennas, dimensions)
+
+	// Part one
+	fmt.Println("Number of unique antinodes:", len(uniqueAntinodes))
+	// Part two
+	fmt.Println("Number of unique antinodes when taking resonant harmonics into account:", len(uniqueResonantAntinodes))
+}