Day 8 part 1

2024/src/main/kotlin/day8.kt

@@ -0,0 +1,42 @@
+fun main() {
+    val grid = Grid.read("day8.txt")
+
+    val antennasByFrequency = mutableMapOf<Char, MutableList<Grid.Coordinate>>()
+    for (y in 0..<grid.height) {
+        for (x in 0..<grid.width) {
+            val value = grid.get(x, y)
+            if (value != '.') {
+                antennasByFrequency.getOrPut(value) { mutableListOf() }.add(Grid.Coordinate(x, y))
+            }
+        }
+    }
+
+    fun isAntinode(coordinate: Grid.Coordinate, frequency: Char, antennas: List<Grid.Coordinate>) =
+        antennas.any { antenna ->
+            val dx = antenna.x - coordinate.x
+            val dy = antenna.y - coordinate.y
+            val secondAntenna = Grid.Coordinate(antenna.x + dx, antenna.y + dy)
+
+            secondAntenna != antenna && grid.inside(secondAntenna) && grid.get(secondAntenna) == frequency
+        }
+
+    fun isAntinode(coordinate: Grid.Coordinate) =
+        antennasByFrequency.any { (frequency, positions) ->
+            isAntinode(coordinate, frequency, positions)
+        }
+
+    val antinodes = mutableSetOf<Grid.Coordinate>()
+
+    for (y in 0..<grid.height) {
+        for (x in 0..<grid.width) {
+
+            val coordinate = Grid.Coordinate(x, y)
+            if (isAntinode(coordinate)) {
+                antinodes.add(coordinate)
+            }
+
+        }
+    }
+
+    println("Part 1: ${antinodes.count()}")
+}

2024/src/main/resources/day8.txt

@@ -0,0 +1,50 @@
+.....................U.........w..................
+l.................................................
+...........o.a................U...w...............
+............................................W.....
+..........T....................s.............7....
+.............................................W....
+.........T..............4....n.d.H.........5......
+......T.....oj...U.....n...w......H...........z...
+.G..x..........................E.....V..H.........
+.........a....................d....s.......7w.....
+...j....r.............o.............V.......d...W.
+.......r..J.Goa.U...............n................z
+.........Jj.........M..........Pv.................
+...J...........t..3..M..............sLV...........
+...................t................n.............
+....r...........X...........M........v............
+...x....t......I......a.PM...............W........
+...........1.Bj....I........vO.h.dL...............
+.........6....Rr......B...X........h..5v.L..z.....
+......1G...........x.....3B.......5...............
+.................B....0..........4..E.............
+.....................X.....5..h....P....f.....D...
+.......1........J.....eK..........................
+..................I....R....K...........k.........
+......G..................O........................
+...........H...9...............K8.P.4..k..E.......
+............1....3.............8.F.............f..
+.........................4........................
+.l...........X............9.......................
+....N.................R...t.e.....................
+...g............3..R.........e....h.........f.....
+...........................e......i...............
+................2...I.7..9..O.....s.........k.....
+....................6...9E.............F..O.......
+........................KN........................
+.......g......................Z.........F..f...Y..
+...........................A....i.................
+...........6g...b........8.......y.....S..........
+..l.....6.....m...............8...................
+....u..m...b...............p...A..................
+..............b.p........................k........
+....m......2...........Z..y....i..................
+........g2.....b.........i....D..ZF...............
+......2.0...........p............N..........A.....
+...m.............S...y........A...Z...N...........
+..S..l..........................................Y.
+........S....0u.................y......DY.........
+...........0.........................D............
+.................u...................p...Y........
+.......u..........................................