d08

day08/d08p1.swift

@@ -0,0 +1,42 @@
+import Foundation
+
+struct Point : Hashable {
+    let x: Int
+    let y: Int
+}
+
+func readInput(_ filePath: String) throws -> (Int, Int, [Character: [Point]]) {
+    let content = try String(contentsOfFile: filePath, encoding: .ascii)
+    let lines = content.split(separator: "\n").map(Array.init)
+    let antennas = lines.enumerated().flatMap { i, line in
+        line.enumerated().compactMap { j, cell in
+            cell == "." ? nil : (cell, i, j)
+        }
+    }
+    var map: [Character: [Point]] = [:]
+    for (type, i, j) in antennas {
+        let current = map[type, default: []]
+        map[type] = current + [Point(x: i, y: j)]
+    }
+    return (lines.count, lines[0].count, map)
+}
+
+func nodes(_ antennas: [Point]) -> Set<Point> {
+    var nodes: Set<Point> = []
+    for i in 0..<antennas.count {
+        for j in i+1..<antennas.count {
+            let (a, b) = (antennas[i], antennas[j])
+            nodes.insert(Point(x: 2*a.x - b.x, y: 2*a.y - b.y))
+            nodes.insert(Point(x: 2*b.x - a.x, y: 2*b.y - a.y))
+        }
+    }
+    return nodes
+}
+
+let (height, width, antennas) = try readInput(CommandLine.arguments[1])
+let answer = antennas
+    .map { c, points in nodes(points) }
+    .reduce(Set([]), { acc, x in acc.union(x) })
+    .filter { p in p.x >= 0 && p.y >= 0 && p.x < height && p.y < width }
+    .count
+print(answer)

day08/d08p2.swift

@@ -0,0 +1,55 @@
+import Foundation
+
+struct Point : Hashable {
+    let x: Int
+    let y: Int
+}
+
+func readInput(_ filePath: String) throws -> (Int, Int, [Character: [Point]]) {
+    let content = try String(contentsOfFile: filePath, encoding: .ascii)
+    let lines = content.split(separator: "\n").map(Array.init)
+    let antennas = lines.enumerated().flatMap { i, line in
+        line.enumerated().compactMap { j, cell in
+            cell == "." ? nil : (cell, i, j)
+        }
+    }
+    var map: [Character: [Point]] = [:]
+    for (type, i, j) in antennas {
+        let current = map[type, default: []]
+        map[type] = current + [Point(x: i, y: j)]
+    }
+    return (lines.count, lines[0].count, map)
+}
+
+func nodes(_ antennas: [Point], h: Int, w: Int) -> Set<Point> {
+    var nodes: Set<Point> = []
+    for i in 0..<antennas.count {
+        for j in i+1..<antennas.count {
+            let (a, b) = (antennas[i], antennas[j])
+            // (k+1)a - kb going one way
+            var k = 0
+            var next = Point(x: (k+1)*a.x - k*b.x, y: (k+1)*a.y - k*b.y)
+            while next.x >= 0 && next.x < h && next.y >= 0 && next.y < w {
+                nodes.insert(next)
+                k += 1
+                next = Point(x: (k+1)*a.x - k*b.x, y: (k+1)*a.y - k*b.y)
+            }
+            // going the other way
+            k = -1
+            next = Point(x: (k+1)*a.x - k*b.x, y: (k+1)*a.y - k*b.y)
+            while next.x >= 0 && next.x < h && next.y >= 0 && next.y < w {
+                nodes.insert(next)
+                k -= 1
+                next = Point(x: (k+1)*a.x - k*b.x, y: (k+1)*a.y - k*b.y)
+            }
+        }
+    }
+    return nodes
+}
+
+let (height, width, antennas) = try readInput(CommandLine.arguments[1])
+let answer = antennas
+    .map { c, points in nodes(points, h: height, w: width) }
+    .reduce(Set([]), { acc, x in acc.union(x) })
+    .count
+print(answer)

day08/input.txt

@@ -0,0 +1,50 @@
+...d............................J.................
+......e.............................J.............
+..........6............7..........................
+........................P7........................
+..................................................
+.........6........................................
+e..........................x.................E....
+...G...A.......d...........................o......
+.....A.e...........................J......8.......
+................6....9.....J.............E.8......
+..........d.9.........7..K....E...................
+...e.....U....9................x..K...............
+......A......O...........P................o.......
+......................x..................M..E.....
+........................x........p................
+........A..................O......................
+.......r.f....O.......P9..G.........m.............
+u...df..r...............7.........................
+.....g.............nXu......N.........K...........
+..............l..........0..............p.........
+.......lu...................p......o..............
+....g..........l........0p..G.....F...............
+.....................................8......F.....
+...................................C..............
+....3................G0......................M....
+2...f....g..........3........P......O......F......
+g......3.....0....H......................F..M.....
+.............c................m...h.....M.........
+...........2....l.................................
+..U...c......2...........................K........
+.D....................r.....f.....................
+....................N.............................
+.U..............h.................................
+...a.............u..............C.................
+c...Uj....a..6...H...................R............
+...3....j................H...............m........
+.......................5.......C..........4....m..
+......................H.........R......N....X.....
+.........h..2.................R................N..
+.......................r...........q...n..........
+.....c..............5.............................
+..a..h....D.................................n.....
+......qk..................D............1.....X....
+.k..................................q.............
+..k..........a.............L................1....4
+......k..........RQ..5.L.j..1..................4..
+..................................................
+..............L.....................oX............
+........Q.............L.........n.................
+...........Q.D........5..........1............4...

day08/test.txt

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