gistfile1.scala

/*
 * Determines if a Sudoku board (a list of lists of Cell case classes containing Options for the
 * cell value) is filled in incorrectly
 */
def isScrewedUp: Boolean = {
  (0 to 8).foldLeft(false) {
    (b, i) => b || rowScrewedUp(i) || colScrewedUp(i) || boxScrewedUp(i)
  }
}

private def rowScrewedUp(rowNum: Int): Boolean = {
  cellsScrewedUp(board(rowNum))
}

private def colScrewedUp(colNum: Int): Boolean = {
  cellsScrewedUp(board.transpose.toSeq(colNum))
}

private def boxScrewedUp(boxNum: Int): Boolean = {
  val boxRow = boxNum / 3
  val boxCol = boxNum % 3

  //Get the relevant rows
  val rows = board.view.slice(boxRow * 3, boxRow * 3 + 3)

  //Take the intersection of the rows with the columns
  val box = rows.map{row => row.slice(boxCol * 3, boxCol * 3 + 3)}.flatten

  cellsScrewedUp(box)
}

private def cellsScrewedUp(set: Seq[Cell]) = {
  val values = set.map {
    cell => cell.value
  }
  val flat = values.flatten
  flat.distinct.size != flat.size
}