matrix.swift

public struct MatrixIndex: BidirectionalIndexType {
  
  public let x, y : Int
  
  private let columns: Int
  
  public func successor() -> MatrixIndex {
    return (x + 1 == columns) ?
      MatrixIndex(x: 0, y: y + 1, columns: columns) :
      MatrixIndex(x: x + 1, y: y, columns: columns)
  }
  
  public func predecessor() -> MatrixIndex {
    return (x == 0) ?
      MatrixIndex(x: columns - 1, y: y - 1, columns: columns) :
      MatrixIndex(x: x - 1, y: y, columns: columns)
  }
}

public func == (lhs: MatrixIndex, rhs: MatrixIndex) -> Bool {
  return lhs.x == rhs.x && lhs.y == rhs.y
}

extension MatrixIndex : CustomDebugStringConvertible {
  public var debugDescription: String {
    return "\(x), \(y)"
  }
}

extension MatrixIndex: RandomAccessIndexType {
  public func advancedBy(n: Int) -> MatrixIndex {
    let total = (y * columns) + x + n
    return MatrixIndex(x: total % columns, y: total / columns, columns: columns)
  }
  public func distanceTo(other: MatrixIndex) -> Int {
    return (other.x - x) + (other.y - y) * columns
  }
}

public struct Matrix2D<T> : MutableCollectionType {
  public var contents: [[T]]
  public subscript(index: MatrixIndex) -> T {
    get {
      return contents[index.y][index.x]
    } set {
      contents[index.y][index.x] = newValue
    }
  }
  public var count: Int { return contents[0].count * contents.count }
  public var startIndex: MatrixIndex {
    return MatrixIndex(x: 0, y: 0, columns: contents[0].count)
  }
  public var endIndex: MatrixIndex {
    return MatrixIndex(x: 0, y: contents.endIndex, columns: contents[0].count)
  }
  public init<
    S : SequenceType where
    S.Generator.Element : SequenceType,
    S.Generator.Element.Generator.Element == T
    >(_ values: S) {
      contents = values.map(Array.init)
      if contents.contains({ $0.endIndex != contents[0].endIndex }) {
        fatalError("All rows do not have the same length")
      }
  }
}

extension Matrix2D : CustomStringConvertible {
  public var description: String {
    return "\n".join(contents.map{String($0)})
  }
}