SquareTiles.scala

object Main {

  def solve(input: Array[Array[Char]]): Option[Array[Array[Char]]] = {
    val width = input(0).length
    val height = input.length

    def isCanCorver(x: Int, y: Int): Boolean = {
      !List((x, y), (x + 1, y), (x, y + 1), (x + 1, y + 1)).exists(
        (v) => v._1 >= width || v._2 >= height || input(v._2)(v._1) != '#'
      )
    }

    def updatePicture(y: Int, x: Int) {
      input(y)(x) = '/'
      input(y + 1)(x) = '\\'
      input(y)(x + 1) = '\\'
      input(y + 1)(x + 1) = '/'
    }

    if (!input.exists(x => x.contains('#'))) {
      Some(input)
    } else {
      (0 until height).foreach(y => {
        (0 until width).foreach(x => {
          if ('#' == input(y)(x) && isCanCorver(x, y)) {
            updatePicture(y, x)
            return solve(input)
          }
        })
      })
      None
    }
  }

  def main(args: Array[String]) {
    val writer = new java.io.PrintWriter("a-large.out")
    try {
      process(io.Source.fromFile("A-large-practice (4).in").getLines)(writer.println)
    } finally {
      writer.flush()
      writer.close()
    }
  }

  def process(lineIn: Iterator[String])(lineOut: String => Unit) = {
    for (i <- 1 to lineIn.next().toInt) {
      val Array(height, row) = lineIn.next().split(" ").map(_.toInt)
      val input = for (y <- 1 to height) yield lineIn.next()

      val result = solve(input.map(x => x.toList.toArray).toArray) match {
        case None => "Impossible"
        case Some(x) => x.map(_.mkString).mkString("\n")
      }

      lineOut(s"Case #$i:\n${result}")
    }
  }
}