SquareTiles.scala

import java.io.FileInputStream
import java.io.FileOutputStream

object SquareTiles extends App {
  def solve(tiles: Array[Array[Char]]): Option[Array[Array[Char]]] = {
    for (
      r <- (0 until (tiles.length - 1));
      c <- (0 until (tiles(r).length - 1))
    ) {
      tiles(r)(c) match {
        case '#' => {
          if (tiles(r)(c + 1) == '#' && tiles(r + 1)(c) == '#' && tiles(r + 1)(c + 1) == '#') {
            tiles(r)(c) = '/'
            tiles(r)(c + 1) = '\\'
            tiles(r + 1)(c) = '\\'
            tiles(r + 1)(c + 1) = '/'
          }
        }
        case _ =>
      }
    }

    if (tiles.flatten.exists(n => n == '#'))
      None
    else
      Some(tiles)
  }
  Console.setIn(new FileInputStream("A-large-practice.in"))
  Console.setOut(new FileOutputStream("A-large-practice.out"))
  val cases = readLine().toInt;
  (1 to cases) foreach { n =>
    val Array(rn, _*) = readLine().split(' ')
    val tiles = (for (r <- (0 until rn.toInt)) yield readLine().toCharArray).toArray
    println(s"Case #$n:")
    println(solve(tiles) match {
      case Some(t) => t.map(_.mkString).mkString("\n")
      case None => "Impossible"
    })
  }
}