d18

day18/d18p1.swift

@@ -0,0 +1,69 @@
+import Foundation
+
+struct Coord : Hashable, CustomStringConvertible {
+    let (x, y): (Int, Int)
+    var description: String { return "(\(x),\(y))" }
+}
+
+func readInput(_ fileName: String) throws -> [Coord] {
+    let xy = try Regex(#"([0-9]+),([0-9]+)"#)
+    return try String(contentsOfFile: fileName,  encoding: .ascii)
+        .split(separator: "\n")
+        .compactMap { $0.wholeMatch(of: xy) }
+        .map { Coord(
+            x: Int($0.output[1].substring!)!,
+            y: Int($0.output[2].substring!)!
+        ) }
+}
+
+struct Map : CustomStringConvertible {
+    let walls: Set<Coord>
+    let (w, h): (Int, Int)
+    var description: String {
+        let top = "   \u{001B}[4m" + (0..<w).map { " \($0 % 10)" }.joined() + "\u{001B}[0m\n"
+        let maze = (0..<h).map { i in
+            String(format: "%2d▕", i) + (0..<w).map { j in
+                walls.contains(Coord(x: j, y: i)) ? "🮘🮘" : "  "
+            }.joined() + "▌"
+        }.joined(separator: "\n")
+        let bot = "\n   " + String(repeating: "🬂", count: w*2) + "🬀"
+        return top + maze + bot
+    }
+
+    func dijkstra(from start: Coord, to end: Coord) -> Int? {
+        var q = Heap<(Coord, Int)>(comparator: { l, r in l.1 < r.1 })
+        var seen: Set<Coord> = [start]
+        q.insert((start, 0))
+        while let (cell, cost) = q.pop() {
+            if cell == end {
+                return cost
+            }
+            [(0, -1), (0, 1), (-1, 0), (1, 0)].map { dy, dx in
+                Coord(x: cell.x + dx, y: cell.y + dy)}
+                .filter { c in c.x >= 0 && c.y >= 0 && c.x < w && c.y < h }
+                .filter { !seen.contains($0) }
+                .filter { !walls.contains($0) }
+                .forEach { neighbor in
+                    seen.insert(neighbor)
+                    q.insert((neighbor, cost + 1))
+                }
+        }
+        return nil
+    }
+}
+
+@main
+struct AoC {
+    static func main() throws {
+        let bytes = try readInput(CommandLine.arguments[1])
+        let w = Int(CommandLine.arguments[2]) ?? 71
+        let h = Int(CommandLine.arguments[3]) ?? 71
+        let limit = Int(CommandLine.arguments[4]) ?? 1024
+        let map = Map(walls: Set(bytes.prefix(limit)), w: w, h: h)
+        print(map)
+        print(map.dijkstra(
+            from: Coord(x: 0, y: 0), to: Coord(x: map.w - 1, y: map.h - 1)
+        ) ?? "no solution")
+    }
+}
+

day18/d18p2.swift

@@ -0,0 +1,76 @@
+import Foundation
+
+struct Coord : Hashable, CustomStringConvertible {
+    let (x, y): (Int, Int)
+    var description: String { return "(\(x),\(y))" }
+}
+
+func readInput(_ fileName: String) throws -> [Coord] {
+    let xy = try Regex(#"([0-9]+),([0-9]+)"#)
+    return try String(contentsOfFile: fileName,  encoding: .ascii)
+        .split(separator: "\n")
+        .compactMap { $0.wholeMatch(of: xy) }
+        .map { Coord(
+            x: Int($0.output[1].substring!)!,
+            y: Int($0.output[2].substring!)!
+        ) }
+}
+
+struct Map : CustomStringConvertible {
+    let walls: Set<Coord>
+    let (w, h): (Int, Int)
+    var description: String {
+        let top = "   \u{001B}[4m" + (0..<w).map { " \($0 % 10)" }.joined() + "\u{001B}[0m\n"
+        let maze = (0..<h).map { i in
+            String(format: "%2d▕", i) + (0..<w).map { j in
+                walls.contains(Coord(x: j, y: i)) ? "██" : "  "
+            }.joined() + "▌"
+        }.joined(separator: "\n")
+        let bot = "\n   " + String(repeating: "🬂", count: w*2) + "🬀"
+        return top + maze + bot
+    }
+
+    func dijkstra(from start: Coord, to end: Coord) -> Int? {
+        var q = Heap<(Coord, Int)>(comparator: { l, r in l.1 < r.1 })
+        var seen: Set<Coord> = [start]
+        q.insert((start, 0))
+        while let (cell, cost) = q.pop() {
+            if cell == end {
+                return cost
+            }
+            [(0, -1), (0, 1), (-1, 0), (1, 0)].map { dy, dx in
+                Coord(x: cell.x + dx, y: cell.y + dy)}
+                .filter { c in c.x >= 0 && c.y >= 0 && c.x < w && c.y < h }
+                .filter { !seen.contains($0) }
+                .filter { !walls.contains($0) }
+                .forEach { neighbor in
+                    seen.insert(neighbor)
+                    q.insert((neighbor, cost + 1))
+                }
+        }
+        return nil
+    }
+}
+
+@main
+struct AoC {
+    static func main() throws {
+        let bytes = try readInput(CommandLine.arguments[1])
+        let w = Int(CommandLine.arguments[2]) ?? 71
+        let h = Int(CommandLine.arguments[3]) ?? 71
+        for limit in 1024..<bytes.count {
+            let map = Map(walls: Set(bytes.prefix(limit)), w: w, h: h)
+            if let cost = map.dijkstra(
+                from: Coord(x: 0, y: 0),
+                to: Coord(x: map.w - 1, y: map.h - 1)
+            ) {
+                print("\(limit): \(cost)")
+            } else {
+                print(map)
+                print("found byte \(limit-1): \(bytes[limit-1])")
+                return
+            }
+        }
+    }
+}
+

day18/heap.swift

@@ -0,0 +1,54 @@
+struct Heap<T> {
+    var comparator: ((_ l: T,_ r: T) -> Bool)
+    var heap: [T] = []
+    var isEmpty: Bool { return heap.isEmpty }
+
+    private mutating func bubbleUp(idx: Int) {
+        let parent = (idx - 1) / 2
+        if idx <= 0 {
+            return
+        }
+        if comparator(heap[idx], heap[parent]) {
+            heap.swapAt(parent, idx)
+            bubbleUp(idx: parent)
+        }
+    }
+
+    private mutating func heapify(_ idx: Int) {
+        let left = idx * 2 + 1
+        let right = idx * 2 + 2
+        var comp = idx
+
+        if heap.count > left && comparator(heap[left], heap[comp]) {
+            comp = left
+        }
+        if heap.count > right && comparator(heap[right], heap[comp]) {
+            comp = right
+        }
+        if comp != idx {
+            heap.swapAt(comp, idx)
+            heapify(comp)
+        }
+    }
+
+    mutating func insert(_ item: T) {
+        heap.append(item)
+        bubbleUp(idx: heap.count-1)
+    }
+
+    mutating func pop() -> T? {
+        let item: T? = heap.first
+        if heap.count == 0 {
+            return nil
+        }
+        if heap.count > 1 {
+            heap[0] = heap[heap.count-1]
+            heap.removeLast()
+            heapify(0)
+        } else if heap.count == 1{
+            heap.removeLast()
+        }
+        return item
+    }
+}
+

day18/test.txt

@@ -0,0 +1,25 @@
+5,4
+4,2
+4,5
+3,0
+2,1
+6,3
+2,4
+1,5
+0,6
+3,3
+2,6
+5,1
+1,2
+5,5
+2,5
+6,5
+1,4
+0,4
+6,4
+1,1
+6,1
+1,0
+0,5
+1,6
+2,0