d15

day15/d15p1.swift

@@ -0,0 +1,97 @@
+import Foundation
+
+enum Move: Character, CustomStringConvertible {
+    case n = "^"
+    case s = "v"
+    case e = ">"
+    case w = "<"
+    var description: String { return String(self.rawValue) }
+    var delta: (Int, Int) {
+        switch self {
+        case .n: return (0, -1)
+        case .s: return (0, 1)
+        case .e: return (1, 0)
+        case .w: return (-1, 0)
+        }
+    }
+}
+
+struct Item: Hashable, CustomStringConvertible {
+    let (x, y): (Int, Int)
+    var description: String { return "(\(x), \(y))" }
+    var gps: Int { return x + 100*y }
+    func move(_ m: Move) -> Item {
+        let (dx, dy) = m.delta
+        return Item(x: x + dx, y: y + dy)
+    }
+}
+
+struct Map: CustomStringConvertible {
+    let walls: Set<Item>
+    var boxes: Set<Item> = []
+    var bot = Item(x: 0, y: 0)
+    var (w, h): (Int, Int)
+    var description: String {
+        var s: [[String]] = Array(
+            repeating: Array(repeating: "  ", count: w*2), count: h
+        )
+        walls.forEach { w in s[w.y][w.x] = "██" }
+        boxes.forEach { b in s[b.y][b.x] = "▒▒" }
+        s[bot.y][bot.x] = "🯅🯅"
+        return s.map { row in row.joined() }.joined(separator: "\n")
+    }
+    var gps: Int { return boxes.reduce(0) { s, box in s + box.gps } }
+
+    init(from s: ArraySlice<String.SubSequence>) {
+        var walls: Set<Item> = []
+        h = s.count
+        w = s[0].count
+        for (y, line) in s.enumerated() {
+            for (x, char) in line.enumerated() {
+                switch char {
+                case "#": walls.insert(Item(x: x, y: y))
+                case "O": boxes.insert(Item(x: x, y: y))
+                case "@": bot = Item(x: x, y: y)
+                default: ()
+                }
+            }
+        }
+        self.walls = walls
+    }
+
+    mutating func move(_ dir: Move) {
+        var pushes: [Item] = []
+        var next = bot.move(dir)
+        while boxes.contains(next) {
+            pushes.append(next)
+            next = next.move(dir)
+        }
+        if !walls.contains(next) {
+            if !pushes.isEmpty { print("pushing box \(pushes)") }
+            pushes.forEach { boxes.remove($0) }
+            pushes.forEach { boxes.insert($0.move(dir)) }
+            bot = bot.move(dir)
+            print("moving bot to \(bot)")
+        } else {
+            print("noop")
+        }
+    }
+}
+
+func readInput(_ filePath: String) throws -> (Map, [Move]) {
+    let content = try String(contentsOfFile: filePath, encoding: .ascii)
+    let lines = content.split(separator: "\n", omittingEmptySubsequences: false)
+    let blankIdx = lines.firstIndex(of: "")!
+    let moves = lines.suffix(from: blankIdx + 1).joined().map { Move(rawValue: $0)! }
+    return (Map(from: lines.prefix(blankIdx)), moves)
+}
+
+var (map, moves) = try readInput(CommandLine.arguments[1])
+print(map)
+print(moves)
+for move in moves {
+    print(move)
+    map.move(move)
+}
+print(map)
+print(map.gps)