Initial commit - at blog post three

.gitignore

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+# Xcode
+#
+# gitignore contributors: remember to update Global/Xcode.gitignore, Objective-C.gitignore & Swift.gitignore
+
+## Build generated
+build/
+DerivedData/
+
+## Various settings
+*.pbxuser
+!default.pbxuser
+*.mode1v3
+!default.mode1v3
+*.mode2v3
+!default.mode2v3
+*.perspectivev3
+!default.perspectivev3
+xcuserdata/
+
+## Other
+*.moved-aside
+*.xcuserstate
+
+## Obj-C/Swift specific
+*.hmap
+*.ipa
+*.dSYM.zip
+*.dSYM
+
+## Playgrounds
+timeline.xctimeline
+playground.xcworkspace
+
+# Swift Package Manager
+#
+# Add this line if you want to avoid checking in source code from Swift Package Manager dependencies.
+# Packages/
+.build/
+
+# CocoaPods
+#
+# We recommend against adding the Pods directory to your .gitignore. However
+# you should judge for yourself, the pros and cons are mentioned at:
+# https://guides.cocoapods.org/using/using-cocoapods.html#should-i-check-the-pods-directory-into-source-control
+#
+# Pods/
+
+# Carthage
+#
+# Add this line if you want to avoid checking in source code from Carthage dependencies.
+# Carthage/Checkouts
+
+Carthage/Build
+
+# fastlane
+#
+# It is recommended to not store the screenshots in the git repo. Instead, use fastlane to re-generate the
+# screenshots whenever they are needed.
+# For more information about the recommended setup visit:
+# https://github.com/fastlane/fastlane/blob/master/fastlane/docs/Gitignore.md
+
+fastlane/report.xml
+fastlane/Preview.html
+fastlane/screenshots
+fastlane/test_output

Pentominoes.playground/Contents.swift

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+//: Playground - noun: a place where people can play
+
+import UIKit
+
+
+
+let board = Board(size: .FiveByTwelve)
+
+let tile = Tile(shape: .O)
+
+for boardSquare in board.squares() {
+    if board.canPositionTile(tile, atSquare: boardSquare) {
+        print("Can position at \(boardSquare)")
+    } 
+}
+
+tile.rotate(true)
+print("Rotated")
+
+for boardSquare in board.squares() {
+    if board.canPositionTile(tile, atSquare: boardSquare) {
+        print("Can position at \(boardSquare)")
+    }
+}
+
+
+
+
+
+

Pentominoes.playground/Sources/Board.swift

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+public class Board: PlayingGrid {
+
+    private (set) public var rows: [[Bool]]
+
+    public struct Size {
+        let height: Int
+        let width: Int
+
+        public static let SixByTen = Size(height: 6, width: 10)
+        public static let FiveByTwelve = Size(height: 5, width: 12)
+        public static let FourByFifteen = Size(height: 4, width: 15)
+        public static let ThreeByTwenty = Size(height: 3, width: 20)
+    }
+
+    public init(size: Size) {
+        // Extend by four "occupied" positions in every direction
+        let paddingHorizontal = [Bool].init(count: 4, repeatedValue: true)
+        let paddingVertical = [Bool].init(count: 8 + size.width, repeatedValue: true)
+        let fullPaddingVertical = [[Bool]].init(count: 4, repeatedValue: paddingVertical)
+        let emptyRow = [Bool].init(count: size.width, repeatedValue: false)
+        rows = fullPaddingVertical
+        for _ in 0..<size.height {
+            rows += [paddingHorizontal + emptyRow + paddingHorizontal]
+        }
+        rows += fullPaddingVertical
+    }
+}
+
+extension Board {
+    public func canPositionTile(tile: Tile, atSquare: Square) -> Bool {
+
+        for tileSquare in tile.squares() {
+            let boardSquare = tileSquare.offsetBy(atSquare)
+            if !squareWithinBoard(boardSquare) {
+                return false
+            }
+            if tileSquare.occupied == true && squareOccupied(boardSquare) {
+                return false
+            }
+        }
+        return true
+    }
+}

Pentominoes.playground/Sources/PlayingGrid.swift

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+public protocol PlayingGrid : CustomStringConvertible, CustomPlaygroundQuickLookable {
+    var rows: [[Bool]] { get }
+    subscript(row: Int) -> [Bool] { get }
+}
+
+extension Bool {
+    var gridCharacter: String {
+        return self ? "#" : "_"
+    }
+}
+
+extension PlayingGrid where Self: protocol<CustomStringConvertible, CustomPlaygroundQuickLookable> {
+    public var description: String {
+        let descriptions : [String] = rows.map { row in
+            row.reduce("") { string, gridValue in
+                string + gridValue.gridCharacter
+            }
+        }
+        return descriptions.joinWithSeparator("\n")
+    }
+    public func customPlaygroundQuickLook() -> PlaygroundQuickLook {
+        return PlaygroundQuickLook(reflecting: description)
+    }
+}
+
+
+public struct Square {
+    let row: Int
+    let column: Int
+    let occupied: Bool?
+
+    public init(row: Int, column: Int, occupied: Bool? = nil) {
+        self.row = row
+        self.column = column
+        self.occupied = occupied
+    }
+
+    func offsetBy(square: Square) -> Square {
+        return Square(row: self.row + square.row, column: self.column + square.column)
+
+    }
+}
+
+public class GridSquareGenerator: GeneratorType {
+    var currentRow: Int = 0
+    var currentColumn: Int = -1
+
+    let grid: PlayingGrid
+
+    public init(grid: PlayingGrid) {
+        self.grid = grid
+    }
+
+    public func next() -> Square? {
+        guard currentRow < grid.rows.count else { return nil }
+
+        currentColumn += 1
+
+        if currentColumn == grid[currentRow].count {
+            currentColumn = 0
+            currentRow += 1
+        }
+        if currentRow < grid.rows.count {
+            return Square(row: currentRow, column: currentColumn, occupied: grid[currentRow][currentColumn])
+        } else {
+            return nil
+        }
+    }
+}
+
+public class GridSquareSequence: SequenceType {
+    let grid: PlayingGrid
+
+    public init(grid: PlayingGrid) {
+        self.grid = grid
+    }
+
+    public func generate() -> GridSquareGenerator {
+        return GridSquareGenerator(grid: grid)
+    }
+}
+
+extension PlayingGrid {
+    public func squares() -> GridSquareSequence {
+        return GridSquareSequence(grid: self)
+    }
+}
+
+
+extension PlayingGrid {
+    public subscript(row: Int) -> [Bool] {
+        get {
+            return rows[row]
+        }
+    }
+
+    public func squareWithinBoard(square: Square) -> Bool {
+        return square.row < rows.count && square.column < rows[square.row].count
+    }
+
+    public func squareOccupied(square: Square) -> Bool {
+        return self[square.row][square.column]
+    }
+}
+
+
+