day 20, part 1

AdventOfCode2020.xcodeproj/project.pbxproj

@@ -26,6 +26,9 @@
 		26DD9C41258DEAC70082D4F2 /* main.swift in Sources */ = {isa = PBXBuildFile; fileRef = 26DD9C40258DEAC70082D4F2 /* main.swift */; };
 		26DD9C58258DEACF0082D4F2 /* LoadData.swift in Sources */ = {isa = PBXBuildFile; fileRef = 26E2AD3A2581713A00702405 /* LoadData.swift */; };
 		26DD9C59258DEACF0082D4F2 /* Extensions.swift in Sources */ = {isa = PBXBuildFile; fileRef = 26E2ACE5257ED09000702405 /* Extensions.swift */; };
+		26DD9C74258F2CEE0082D4F2 /* main.swift in Sources */ = {isa = PBXBuildFile; fileRef = 26DD9C73258F2CEE0082D4F2 /* main.swift */; };
+		26DD9C8C258F2CF80082D4F2 /* LoadData.swift in Sources */ = {isa = PBXBuildFile; fileRef = 26E2AD3A2581713A00702405 /* LoadData.swift */; };
+		26DD9C8D258F2CF80082D4F2 /* Extensions.swift in Sources */ = {isa = PBXBuildFile; fileRef = 26E2ACE5257ED09000702405 /* Extensions.swift */; };
 		26E2ACD8257ECFFA00702405 /* main.swift in Sources */ = {isa = PBXBuildFile; fileRef = 26E2ACD7257ECFFA00702405 /* main.swift */; };
 		26E2ACE6257ED09000702405 /* Extensions.swift in Sources */ = {isa = PBXBuildFile; fileRef = 26E2ACE5257ED09000702405 /* Extensions.swift */; };
 		26E2ACE7257ED09000702405 /* Extensions.swift in Sources */ = {isa = PBXBuildFile; fileRef = 26E2ACE5257ED09000702405 /* Extensions.swift */; };
@@ -166,6 +169,15 @@
 			);
 			runOnlyForDeploymentPostprocessing = 1;
 		};
+		26DD9C6F258F2CEE0082D4F2 /* CopyFiles */ = {
+			isa = PBXCopyFilesBuildPhase;
+			buildActionMask = 2147483647;
+			dstPath = /usr/share/man/man1/;
+			dstSubfolderSpec = 0;
+			files = (
+			);
+			runOnlyForDeploymentPostprocessing = 1;
+		};
 		26E2ACD3257ECFFA00702405 /* CopyFiles */ = {
 			isa = PBXCopyFilesBuildPhase;
 			buildActionMask = 2147483647;
@@ -263,6 +275,8 @@
 		26BD88A4258C818300E92A8E /* main.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = main.swift; sourceTree = "<group>"; };
 		26DD9C3E258DEAC70082D4F2 /* day19 */ = {isa = PBXFileReference; explicitFileType = "compiled.mach-o.executable"; includeInIndex = 0; path = day19; sourceTree = BUILT_PRODUCTS_DIR; };
 		26DD9C40258DEAC70082D4F2 /* main.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = main.swift; sourceTree = "<group>"; };
+		26DD9C71258F2CEE0082D4F2 /* day20 */ = {isa = PBXFileReference; explicitFileType = "compiled.mach-o.executable"; includeInIndex = 0; path = day20; sourceTree = BUILT_PRODUCTS_DIR; };
+		26DD9C73258F2CEE0082D4F2 /* main.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = main.swift; sourceTree = "<group>"; };
 		26E2ACD5257ECFFA00702405 /* day8 */ = {isa = PBXFileReference; explicitFileType = "compiled.mach-o.executable"; includeInIndex = 0; path = day8; sourceTree = BUILT_PRODUCTS_DIR; };
 		26E2ACD7257ECFFA00702405 /* main.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = main.swift; sourceTree = "<group>"; };
 		26E2ACE5257ED09000702405 /* Extensions.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Extensions.swift; sourceTree = "<group>"; };
@@ -361,6 +375,13 @@
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
+		26DD9C6E258F2CEE0082D4F2 /* Frameworks */ = {
+			isa = PBXFrameworksBuildPhase;
+			buildActionMask = 2147483647;
+			files = (
+			);
+			runOnlyForDeploymentPostprocessing = 0;
+		};
 		26E2ACD2257ECFFA00702405 /* Frameworks */ = {
 			isa = PBXFrameworksBuildPhase;
 			buildActionMask = 2147483647;
@@ -459,6 +480,7 @@
 				26BD8863258B2D5300E92A8E /* day17 */,
 				26BD88A3258C818300E92A8E /* day18 */,
 				26DD9C3F258DEAC70082D4F2 /* day19 */,
+				26DD9C72258F2CEE0082D4F2 /* day20 */,
 				268D953A25781DD80030EC4D /* Products */,
 			);
 			sourceTree = "<group>";
@@ -485,6 +507,7 @@
 				26BD8862258B2D5300E92A8E /* day17 */,
 				26BD88A2258C818300E92A8E /* day18 */,
 				26DD9C3E258DEAC70082D4F2 /* day19 */,
+				26DD9C71258F2CEE0082D4F2 /* day20 */,
 			);
 			name = Products;
 			sourceTree = "<group>";
@@ -561,6 +584,14 @@
 			path = day19;
 			sourceTree = "<group>";
 		};
+		26DD9C72258F2CEE0082D4F2 /* day20 */ = {
+			isa = PBXGroup;
+			children = (
+				26DD9C73258F2CEE0082D4F2 /* main.swift */,
+			);
+			path = day20;
+			sourceTree = "<group>";
+		};
 		26E2ACD6257ECFFA00702405 /* day8 */ = {
 			isa = PBXGroup;
 			children = (
@@ -824,6 +855,23 @@
 			productReference = 26DD9C3E258DEAC70082D4F2 /* day19 */;
 			productType = "com.apple.product-type.tool";
 		};
+		26DD9C70258F2CEE0082D4F2 /* day20 */ = {
+			isa = PBXNativeTarget;
+			buildConfigurationList = 26DD9C77258F2CEE0082D4F2 /* Build configuration list for PBXNativeTarget "day20" */;
+			buildPhases = (
+				26DD9C6D258F2CEE0082D4F2 /* Sources */,
+				26DD9C6E258F2CEE0082D4F2 /* Frameworks */,
+				26DD9C6F258F2CEE0082D4F2 /* CopyFiles */,
+			);
+			buildRules = (
+			);
+			dependencies = (
+			);
+			name = day20;
+			productName = day20;
+			productReference = 26DD9C71258F2CEE0082D4F2 /* day20 */;
+			productType = "com.apple.product-type.tool";
+		};
 		26E2ACD4257ECFFA00702405 /* day8 */ = {
 			isa = PBXNativeTarget;
 			buildConfigurationList = 26E2ACDB257ECFFA00702405 /* Build configuration list for PBXNativeTarget "day8" */;
@@ -1002,6 +1050,9 @@
 					26DD9C3D258DEAC70082D4F2 = {
 						CreatedOnToolsVersion = 12.3;
 					};
+					26DD9C70258F2CEE0082D4F2 = {
+						CreatedOnToolsVersion = 12.3;
+					};
 					26E2ACD4257ECFFA00702405 = {
 						CreatedOnToolsVersion = 12.2;
 					};
@@ -1060,6 +1111,7 @@
 				26BD8861258B2D5300E92A8E /* day17 */,
 				26BD88A1258C818300E92A8E /* day18 */,
 				26DD9C3D258DEAC70082D4F2 /* day19 */,
+				26DD9C70258F2CEE0082D4F2 /* day20 */,
 			);
 		};
 /* End PBXProject section */
@@ -1175,6 +1227,16 @@
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
+		26DD9C6D258F2CEE0082D4F2 /* Sources */ = {
+			isa = PBXSourcesBuildPhase;
+			buildActionMask = 2147483647;
+			files = (
+				26DD9C74258F2CEE0082D4F2 /* main.swift in Sources */,
+				26DD9C8D258F2CF80082D4F2 /* Extensions.swift in Sources */,
+				26DD9C8C258F2CF80082D4F2 /* LoadData.swift in Sources */,
+			);
+			runOnlyForDeploymentPostprocessing = 0;
+		};
 		26E2ACD1257ECFFA00702405 /* Sources */ = {
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
@@ -1633,6 +1695,28 @@
 			};
 			name = Release;
 		};
+		26DD9C75258F2CEE0082D4F2 /* Debug */ = {
+			isa = XCBuildConfiguration;
+			buildSettings = {
+				CODE_SIGN_STYLE = Automatic;
+				DEVELOPMENT_TEAM = 722B335UM5;
+				ENABLE_HARDENED_RUNTIME = YES;
+				PRODUCT_NAME = "$(TARGET_NAME)";
+				SWIFT_VERSION = 5.0;
+			};
+			name = Debug;
+		};
+		26DD9C76258F2CEE0082D4F2 /* Release */ = {
+			isa = XCBuildConfiguration;
+			buildSettings = {
+				CODE_SIGN_STYLE = Automatic;
+				DEVELOPMENT_TEAM = 722B335UM5;
+				ENABLE_HARDENED_RUNTIME = YES;
+				PRODUCT_NAME = "$(TARGET_NAME)";
+				SWIFT_VERSION = 5.0;
+			};
+			name = Release;
+		};
 		26E2ACD9257ECFFA00702405 /* Debug */ = {
 			isa = XCBuildConfiguration;
 			buildSettings = {
@@ -1936,6 +2020,15 @@
 			defaultConfigurationIsVisible = 0;
 			defaultConfigurationName = Release;
 		};
+		26DD9C77258F2CEE0082D4F2 /* Build configuration list for PBXNativeTarget "day20" */ = {
+			isa = XCConfigurationList;
+			buildConfigurations = (
+				26DD9C75258F2CEE0082D4F2 /* Debug */,
+				26DD9C76258F2CEE0082D4F2 /* Release */,
+			);
+			defaultConfigurationIsVisible = 0;
+			defaultConfigurationName = Release;
+		};
 		26E2ACDB257ECFFA00702405 /* Build configuration list for PBXNativeTarget "day8" */ = {
 			isa = XCConfigurationList;
 			buildConfigurations = (

day20/main.swift

@@ -0,0 +1,196 @@
+import Foundation
+
+let input = loadData(day: 20)
+let scanner = Scanner(string: input)
+
+
+struct Tile {
+    var id: Int
+    var imageData: [Bool]
+    var size: Int
+
+    subscript (_ x: Int, _ y: Int) -> Bool {
+        get { imageData[x + y * size] }
+        set { imageData[x + y * size] = newValue }
+    }
+}
+
+
+extension Scanner {
+    func tile() -> Tile? {
+        guard string("Tile"),
+              let id = scanInt(),
+              string(":"),
+              let (image, size) = imageData()
+        else { return nil }
+        return Tile(id: id, imageData: image, size: size)
+    }
+
+    func imageData() -> ([Bool], Int)? {
+        var result: [Bool] = []
+        let set = CharacterSet(charactersIn: "#.")
+        var width: Int? = nil
+        while let line = scanCharacters(from: set) {
+            assert(width == nil || line.count == width)
+            width = line.count
+            result.append(contentsOf: line.map { $0 == "#" })
+        }
+
+        guard let w = width else { return nil }
+
+        return (result, w)
+    }
+
+    func tileSet() -> [Int: Tile]? {
+        var result: [Int: Tile] = [:]
+        while !isAtEnd {
+            guard let tile = self.tile() else { return nil }
+            result[tile.id] = tile
+        }
+        return result
+    }
+}
+
+let tilesById = scanner.tileSet()!
+
+struct TileReference: Hashable {
+    enum Rotation: CaseIterable {
+        case rotate0, rotate90, rotate180, rotate270
+    }
+
+    var id: Int
+    var flipped: Bool
+    var rotation: Rotation
+
+    subscript (x: Int, y: Int) -> Bool {
+        get {
+            let tile = tilesById[id]!
+
+            var coord = flipped ? (x: tile.size - 1 - x, y: y) : (x: x, y: y)
+            coord = rotation.get(x: coord.x, y: coord.y, size: tile.size)
+
+            return tile[coord.x, coord.y]
+        }
+    }
+
+    var end: Int { tilesById[id]!.size - 1 }
+}
+
+extension TileReference.Rotation {
+    func get(x: Int, y: Int, size: Int) -> (x: Int, y: Int) {
+        let e = size - 1
+        switch self {
+        case .rotate0: return (x, y)
+        case .rotate90: return (y, e - x)
+        case .rotate180: return (x, e - y)
+        case .rotate270: return (e - y, x)
+        }
+    }
+}
+
+struct Board {
+    struct Cell {
+        var possible: Array<TileReference>
+    }
+
+    var size: Int
+    var cells: [Cell]
+
+    init<T>(tiles: T) where T: Sequence, T.Element == Int {
+        let orientations = [true, false].flatMap { flipped in TileReference.Rotation.allCases.map { (flipped, $0) } }
+        let allOptions = tiles.flatMap { id in orientations.map { TileReference(id: id, flipped: $0.0, rotation: $0.1 ) } }
+        size = Int(sqrt(Double(tilesById.count)))
+        cells = Array(repeating: Cell(possible: allOptions), count: size*size)
+        assert(size * size == tilesById.count)
+    }
+
+    subscript(x: Int, y: Int) -> Cell {
+        get { cells[x + y * size] }
+        set { cells[x + y * size] = newValue }
+    }
+
+    func coordinate(_ cell: Int) -> (x: Int, y: Int) {
+        let (y, x) = cell.quotientAndRemainder(dividingBy: size)
+        return (x, y)
+    }
+
+    func solve(startingAt: Int = 0) -> Board? {
+        if startingAt >= cells.count { return self }
+
+        let coord = coordinate(startingAt)
+        let left = coord.x > 0 ? self[coord.x - 1, coord.y].chosen! : nil
+        let above = coord.y > 0 ? self[coord.x, coord.y - 1].chosen! : nil
+
+        func matchLeft(_ ref: TileReference) -> Bool {
+            guard let left = left else { return true }
+            return (0...ref.end).allSatisfy { left[left.end, $0] == ref[0, $0] }
+        }
+
+        func matchAbove(_ ref: TileReference) -> Bool {
+            guard let above = above else { return true }
+            return (0...ref.end).allSatisfy { above[$0, above.end] == ref[$0, 0] }
+        }
+
+        for option in cells[startingAt].possible.lazy.filter({ matchLeft($0) && matchAbove($0) }) {
+            var result = self
+            result.cells[startingAt].possible = [option]
+
+            let next = startingAt + 1
+
+            for cell in next..<cells.count {
+                result.cells[cell].possible = result.cells[cell].possible.filter {
+                    return $0.id != option.id
+                }
+
+                if result.cells[cell].possible.isEmpty {
+                    return nil
+                }
+            }
+
+            if let solution = result.solve(startingAt: next) {
+                return solution
+            }
+        }
+
+        return nil
+    }
+}
+
+
+extension Board.Cell {
+    var chosen: TileReference? {
+        guard let result = possible.first, possible.count == 1 else {
+            return nil
+        }
+
+        return result
+    }
+}
+
+guard let solution = Board(tiles: tilesById.keys).solve() else { fatalError() }
+
+let e = solution.size - 1
+let ts = tilesById.first!.value.size
+
+for y in 0...e {
+    for l in 0..<ts {
+        for x in 0...e {
+            let tile = solution[x, y].chosen!
+            for c in 0..<ts {
+                print(tile[c,l] ? "#" : ".", terminator: "")
+            }
+            print(terminator: " ")
+        }
+        print()
+    }
+    print()
+}
+
+print()
+
+print(
+    solution[0,0].chosen!.id *
+    solution[e,0].chosen!.id *
+    solution[0,e].chosen!.id *
+    solution[e,e].chosen!.id
+)