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Forked from pathikrit/SudokuSolver.scala
Created July 27, 2018 17:19
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Sudoku Solver in Scala
val n = 9
val s = Math.sqrt(n).toInt
type Board = IndexedSeq[IndexedSeq[Int]]
def solve(board: Board, cell: Int = 0): Option[Board] = (cell%n, cell/n) match {
case (r, `n`) => Some(board)
case (r, c) if board(r)(c) > 0 => solve(board, cell + 1)
case (r, c) =>
def cells(i: Int) = Seq(board(r)(i), board(i)(c), board(s*(r/s) + i/s)(s*(c/s) + i%s))
def guess(x: Int) = solve(board.updated(r, board(r).updated(c, x)), cell + 1)
val used = board.indices flatMap cells
1 to n diff used collectFirst Function.unlift(guess)
}
//////////////////////////////////////////////////////////////////
import scala.collection.{IndexedSeq => $}
val board = $( //0s denote empty cells
$(1, 0, 0, 0, 0, 7, 0, 9, 0),
$(0, 3, 0, 0, 2, 0, 0, 0, 8),
$(0, 0, 9, 6, 0, 0, 5, 0, 0),
$(0, 0, 5, 3, 0, 0, 9, 0, 0),
$(0, 1, 0, 0, 8, 0, 0, 0, 2),
$(6, 0, 0, 0, 0, 4, 0, 0, 0),
$(3, 0, 0, 0, 0, 0, 0, 1, 0),
$(0, 4, 0, 0, 0, 0, 0, 0, 7),
$(0, 0, 7, 0, 0, 0, 3, 0, 0)
)
println(solve(board).get.map(_ mkString " ") mkString "\n")
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