Day 23

AoC21.xcodeproj/project.pbxproj

@@ -7,6 +7,8 @@
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+		26132D2B2774C871004F0228 /* day23.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = day23.swift; sourceTree = "<group>"; };
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@@ -238,6 +251,13 @@
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 				2680ECE22771D82400CAB23C /* day21.swift */,
 				2680ECDF2770A2FC00CAB23C /* day20.swift */,
@@ -405,6 +426,7 @@
 				2680ECD82770A2E900CAB23C /* Day20 */,
 				2680ECE72771D82F00CAB23C /* Day21 */,
 				2680ECF427732A8300CAB23C /* Day22 */,
+				26132D302774C87D004F0228 /* Day23 */,
 			);
 			name = Products;
 			sourceTree = "<group>";
@@ -412,6 +434,23 @@
 /* End PBXGroup section */
 
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+				26132D2D2774C87D004F0228 /* Frameworks */,
+				26132D2E2774C87D004F0228 /* CopyFiles */,
+			);
+			buildRules = (
+			);
+			dependencies = (
+			);
+			name = Day23;
+			productName = Day23;
+			productReference = 26132D302774C87D004F0228 /* Day23 */;
+			productType = "com.apple.product-type.tool";
+		};
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@@ -712,6 +751,9 @@
 				LastUpgradeCheck = 1310;
 				ORGANIZATIONNAME = 5sw;
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@@ -806,11 +848,21 @@
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 				2680ECE62771D82F00CAB23C /* Day21 */,
 				2680ECF327732A8300CAB23C /* Day22 */,
+				26132D2F2774C87D004F0228 /* Day23 */,
 			);
 		};
 /* End PBXProject section */
 
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+				26132D382774C886004F0228 /* common.swift in Sources */,
+			);
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+		};
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+				CODE_SIGN_STYLE = Automatic;
+				DEVELOPMENT_TEAM = 722B335UM5;
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+			name = Debug;
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+		26132D362774C87D004F0228 /* Release */ = {
+			isa = XCBuildConfiguration;
+			buildSettings = {
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+				DEVELOPMENT_TEAM = 722B335UM5;
+				ENABLE_HARDENED_RUNTIME = YES;
+				MACOSX_DEPLOYMENT_TARGET = 12.1;
+				PRODUCT_NAME = "$(TARGET_NAME)";
+				SWIFT_VERSION = 5.0;
+			};
+			name = Release;
+		};
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+			defaultConfigurationName = Release;
+		};
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day23.swift

@@ -0,0 +1,284 @@
+
+@main
+struct Day23: Puzzle {
+    func run() {
+        part1()
+        part2()
+    }
+
+    func part1() {
+        var board = Board(height: 3)
+        board.fillHomeRow(for: .a, pieces: [.c, .c])
+        board.fillHomeRow(for: .b, pieces: [.b, .d])
+        board.fillHomeRow(for: .c, pieces: [.a, .a])
+        board.fillHomeRow(for: .d, pieces: [.d, .b])
+        board.show()
+        print("Part 1:", find(start: board))
+    }
+
+    func part2() {
+        var board = Board(height: 5)
+        board.fillHomeRow(for: .a, pieces: [.c, .d, .d, .c])
+        board.fillHomeRow(for: .b, pieces: [.b, .c, .b, .d])
+        board.fillHomeRow(for: .c, pieces: [.a, .b, .a, .a])
+        board.fillHomeRow(for: .d, pieces: [.d, .a, .c, .b])
+        board.show()
+        print("Part 2:", find(start: board))
+    }
+
+    func find(start: Board) -> Int {
+        let target = Board.makeGoal(height: start.height)
+        var current = start
+        var totalCost = 0
+
+        var possible: [Board: Int] = [:]
+        var visited: Set<Board> = []
+
+
+        while current != target {
+            visited.insert(current)
+
+            for (next, cost) in current.possibleMoves() where !visited.contains(next) {
+                possible[next] = min(possible[next, default: .max], totalCost + cost)
+            }
+
+            (current, totalCost) = possible.min { $0.value < $1.value }!
+
+            possible.removeValue(forKey: current)
+        }
+
+        return totalCost
+    }
+
+}
+
+struct Board: Hashable {
+    enum Piece: CaseIterable, Hashable, CustomStringConvertible {
+        case a, b, c, d
+
+        var homeColumn: Int {
+            switch self {
+            case .a:
+                return 2
+            case .b:
+                return 4
+            case .c:
+                return 6
+            case .d:
+                return 8
+            }
+        }
+
+        var cost: Int {
+            switch self {
+            case .a:
+                return 1
+            case .b:
+                return 10
+            case .c:
+                return 100
+            case .d:
+                return 1000
+            }
+        }
+
+        var sign: Character {
+            switch self {
+            case .a:
+                return "A"
+            case .b:
+                return "B"
+            case .c:
+                return "C"
+            case .d:
+                return "D"
+            }
+        }
+
+        var description: String { String(sign) }
+    }
+    enum Cell: Hashable {
+        case piece(Piece)
+        case empty
+        case outside
+    }
+
+    var width = 11
+    var height = 3
+
+    var board: [Cell]
+
+    init(height: Int) {
+        self.height = height
+        board = Array(repeating: .outside, count: width * height)
+        for x in 0..<width {
+            self[x, 0] = .empty
+        }
+    }
+
+    mutating func fillHomeRow(for piece: Piece, pieces: [Piece]) {
+        precondition(pieces.count == height - 1)
+        let x = piece.homeColumn
+        for (y, piece) in pieces.enumerated() {
+            self[x, y + 1] = .piece(piece)
+        }
+    }
+
+    static func makeGoal(height: Int) -> Self {
+        var board = Self(height: height)
+        for piece in Piece.allCases {
+            for y in 1..<board.height {
+                board[piece.homeColumn, y] = .piece(piece)
+            }
+        }
+        return board
+    }
+
+    func movablePieces() -> [(Piece, Int, Int)] {
+        var result: [(Piece, Int, Int)] = []
+        for x in 0..<width {
+            if case .piece(let piece) = self[x, 0] {
+                result.append((piece, x, 0))
+            }
+        }
+
+        for home in Piece.allCases {
+            let x = home.homeColumn
+            var y = 1
+            while y < height, case .empty = self[x, y] {
+                y += 1
+            }
+            if y < height, case let .piece(piece) = self[x, y] {
+                result.append((piece, x, y))
+            }
+        }
+
+        return result
+    }
+
+    func possibleMoves() -> [(Board, Int)] {
+        let pieces = movablePieces()
+            .filter { !isHome(piece: $0.0, x: $0.1, y: $0.2) }
+
+        var result: [(Board, Int)] = []
+        for (piece, x, y) in pieces {
+            if let newY = freeHomeRowPosition(piece: piece), freeCorridor(from: x, to: piece.homeColumn) {
+                result.append(move(piece: piece, from: (x, y), to: (piece.homeColumn, newY)))
+            }
+
+            for newX in openCorridorPositions(x: x) {
+                result.append(move(piece: piece, from: (x, y), to: (newX, 0)))
+            }
+        }
+
+        return result
+    }
+
+    func freeCorridor(from x0: Int, to x1: Int) -> Bool {
+        let minX: Int
+        let maxX: Int
+
+        if x0 < x1 { (minX, maxX) = (x0 + 1, x1) }
+        else { (minX, maxX) = (x1, x0 - 1) }
+
+        for x in minX...maxX {
+            if self[x, 0] != .empty {
+                return false
+            }
+        }
+
+        return true
+    }
+
+    func move(piece: Piece, from: (Int, Int), to: (Int, Int)) -> (Board, Int) {
+        let (x, y) = from
+        let (newX, newY) = to
+
+        precondition(self[newX,newY] == .empty)
+
+        let cost = (y + distance((x, 0), (newX, newY))) * piece.cost
+        var board = self
+        board[x, y] = .empty
+        board[newX, newY] = .piece(piece)
+
+        return (board, cost)
+    }
+
+    func freeHomeRowPosition(piece: Piece) -> Int? {
+        let x = piece.homeColumn
+        var depth = height - 1
+
+    loop: while depth > 0 {
+        switch self[x, depth] {
+        case .piece(piece): break
+        case .piece: return nil
+        case .empty: break loop
+        case .outside: preconditionFailure("Invalid board")
+        }
+        depth -= 1
+    }
+
+        return depth
+    }
+
+    static let homeColumns = Set(Piece.allCases.map(\.homeColumn))
+
+    func openCorridorPositions(x: Int) -> [Int] {
+        var xmin = x
+        var xmax = x
+
+        while xmin > 0 && self[xmin, 0] == .empty {
+            xmin -= 1
+        }
+
+        while xmax < width && self[xmax, 0] == .empty {
+            xmax += 1
+        }
+
+        let result = (xmin..<xmax).filter { !Self.homeColumns.contains($0) && self[$0,0] ==  .empty }
+        return result
+    }
+
+    func distance(_ a: (Int, Int), _ b: (Int, Int)) -> Int {
+        let (x0, y0) = a
+        let (x1, y1) = b
+
+        return abs(x1 - x0) + abs(y1 - y0)
+    }
+
+    func isHome(piece: Piece, x: Int, y: Int)  -> Bool {
+        guard x == piece.homeColumn && y > 0 else { return false }
+        for otherY in (y + 1)..<height {
+            if self[x, otherY] != .piece(piece) {
+                return false
+            }
+        }
+        return true
+    }
+
+    func show() {
+        print(String(repeating: "#", count: width + 2))
+        for y in 0..<height {
+            var line = ""
+            for x in 0..<width {
+                switch self[x, y] {
+                case .outside:
+                    line += "#"
+                case .empty: line += "."
+                case .piece(let piece): line.append(piece.sign)
+                }
+            }
+            print("#\(line)#")
+        }
+        print(String(repeating: "#", count: width + 2))
+    }
+
+    subscript(x: Int, y: Int) -> Cell {
+        get {
+            board[x + width * y]
+        }
+        set {
+            board[x + width * y] = newValue
+        }
+    }
+}