use a heap for marginally faster execution

day16/d16p1.swift

@@ -58,7 +58,7 @@ struct Maze : CustomStringConvertible {
         let s: [[String]] = walls.enumerated().map { i, r in
             [String(format: "%3d ", i)] + r.map { $0 ? "██" : "  " }
         }
-        print("    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4")
+        print("    " + (0..<w).map { " \($0 % 10)" }.joined())
         return s.map { $0.joined() }.joined(separator: "\n")
     }
     init(fromFile f: String) throws {
@@ -111,10 +111,10 @@ struct Maze : CustomStringConvertible {
         let edges = graph()
         // edges.forEach { k, v in print(" - \(k): \(v)") }
 
-        var q: [CellCost] = [(cell: start, cost: 0)]
+        var q = Heap<CellCost>(comparator: { $0.cost < $1.cost })
+        q.insert((cell: start, cost: 0))
         var visited: [Cell:Int] = [:]
-        while !q.isEmpty {
-            let e = q.removeLast()
+        while let e = q.pop() {
             if let node = edges[e.cell] {
                 for (cell, cost) in node {
                     if let prevCost = visited[cell] {
@@ -123,7 +123,7 @@ struct Maze : CustomStringConvertible {
                         }
                     }
                     visited[cell] = e.cost + cost
-                    q.append((cell: cell, cost: e.cost + cost))
+                    q.insert((cell: cell, cost: e.cost + cost))
                 }
             }
         }
@@ -131,6 +131,12 @@ struct Maze : CustomStringConvertible {
     }
 }
 
-let maze = try Maze(fromFile: CommandLine.arguments[1])
-// print(maze)
-print(maze.search())
+@main
+struct AoC {
+    static func main() throws {
+        let maze = try Maze(fromFile: CommandLine.arguments[1])
+        print(maze)
+        print("minCost: \(maze.search())")
+    }
+}
+

day16/d16p2.swift

@@ -1,6 +1,7 @@
 import Foundation
 
 typealias CellCost = (cell: Cell, cost: Int)
+typealias PathCostFromStart = [Cell:(Int, [Cell])]
 
 enum Dir : String, CaseIterable, CustomStringConvertible {
     case n = "▲"
@@ -35,39 +36,31 @@ struct Cell : Hashable, CustomStringConvertible {
     }
 }
 
-struct QueueEntry : Hashable, CustomStringConvertible {
+struct QueueEntry : Hashable {
     let cell: Cell
     let origin: Cell
     let costSoFar: Int
     let path: [Cell]
-    var description: String { return "\(cell) from \(origin) @\(costSoFar)" }
 }
 
-struct CellPair : Hashable, CustomStringConvertible {
+struct CellPair : Hashable {
     let a: Cell
     let b: Cell
-    var description: String { return "\(a),\(b)" }
 }
 
-struct Maze : CustomStringConvertible {
+struct Maze {
     let walls: [[Bool]]
     let (w, h): (Int, Int)
-    var start: Cell { return Cell(i: h-2, j: 1, dir: Dir.e) }
-    var ends: Set<Cell> {
-        return Set(Dir.allCases.map { Cell(i: 1, j: w-2, dir: $0) })
-    }
-    var description: String {
-        let s: [[String]] = walls.enumerated().map { i, r in
-            [String(format: "%3d ", i)] + r.map { $0 ? "██" : "  " }
-        }
-        print("    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4")
-        return s.map { $0.joined() }.joined(separator: "\n")
-    }
+    let start: Cell
+    let ends: Set<Cell>
     init(fromFile f: String) throws {
         let content = try String(contentsOfFile: f, encoding: .ascii)
         let lines = content.split(separator: "\n")
-        (h, w) = (lines.count, lines[0].count)
+        let (h, w) = (lines.count, lines[0].count)
+        (self.h, self.w) = (h, w)
         walls = lines.map { line in line.map { cell in cell == "#" } }
+        start = Cell(i: h-2, j: 1, dir: Dir.e)
+        ends = Set(Dir.allCases.map { Cell(i: 1, j: w-2, dir: $0) })
     }
 
     func neighbors(of cell: Cell) -> [CellCost] {
@@ -114,11 +107,11 @@ struct Maze : CustomStringConvertible {
 
 }
 
-func search(graph edges: [Cell:[CellCost]], start: Cell) -> [Cell:(Int, [Cell])] {
-    var q: [CellCost] = [(cell: start, cost: 0)]
-    var visited: [Cell:(Int, [Cell])] = [:]
-    while !q.isEmpty {
-        let e = q.removeLast()
+func search(graph edges: [Cell:[CellCost]], start: Cell) -> PathCostFromStart {
+    var q = Heap<CellCost>(comparator: { l, r in l.cost < r.cost })
+    q.insert((cell: start, cost: 0))
+    var visited: PathCostFromStart = [:]
+    while let e = q.pop() {
         if let node = edges[e.cell] {
             for (cell, cost) in node {
                 let newCost = e.cost + cost
@@ -132,14 +125,14 @@ func search(graph edges: [Cell:[CellCost]], start: Cell) -> [Cell:(Int, [Cell])]
                     }
                 }
                 visited[cell] = (newCost, [e.cell])
-                q.append((cell: cell, cost: newCost))
+                q.insert((cell: cell, cost: newCost))
             }
         }
     }
     return visited
 }
 
-func trace(_ visited: [Cell:(Int, [Cell])], from: Cell, to: Cell) -> [[Cell]] {
+func trace(_ visited: PathCostFromStart, from: Cell, to: Cell) -> [[Cell]] {
     if from == to {
         return [[from]]
     }
@@ -148,16 +141,22 @@ func trace(_ visited: [Cell:(Int, [Cell])], from: Cell, to: Cell) -> [[Cell]] {
     }
 }
 
-let maze = try Maze(fromFile: CommandLine.arguments[1])
-let (graph, pathPairs) = maze.graph()
-let visited = search(graph: graph, start: maze.start)
-let minCost = maze.ends.compactMap { visited[$0] }.map { $0.0 }.min()!
-print("minCost: \(minCost)")
-let seats = maze.ends
-    .filter { visited[$0, default: (0, [])].0 == minCost }
-    .flatMap { trace(visited, from: $0, to: maze.start) }
-    .map { zip($0, $0.dropFirst()) }
-    .map { $0.flatMap { pathPairs[CellPair(a: $0.0, b: $0.1)]! } }
-    .map { $0.map { cell in Cell(i: cell.i, j: cell.j, dir: Dir.n) } }
-    .flatMap { $0 }
-print("seats: \(Set(seats).count)")
+@main
+struct AoC {
+    static func main() throws {
+        let maze = try Maze(fromFile: CommandLine.arguments[1])
+        let (graph, pathPairs) = maze.graph()
+        let visited = search(graph: graph, start: maze.start)
+        let minCost = maze.ends.compactMap { visited[$0] }.map { $0.0 }.min()!
+        print("minCost: \(minCost)")
+        let seats = maze.ends
+            .filter { visited[$0, default: (0, [])].0 == minCost }
+            .flatMap { trace(visited, from: $0, to: maze.start) }
+            .map { zip($0, $0.dropFirst()) }
+            .map { $0.flatMap { pathPairs[CellPair(a: $0.0, b: $0.1)]! } }
+            .map { $0.map { cell in Cell(i: cell.i, j: cell.j, dir: Dir.n) } }
+            .flatMap { $0 }
+        print("seats: \(Set(seats).count)")
+    }
+}
+

day16/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
+    }
+}
+