straight forward solution to the Lost Pawn Solver

LostPawnSolver.scala

def solve(board: Seq[Seq[Seq[Int]]]): String = {
  require(board.size == 7 && board.forall(row => row.size == 8 && row.forall(_.size == 3)),"Must have exact dimensions")

  //initialization
  val mat = new Array[Array[(Int,Char)]](8)
  for(i ← 0 to 7){
    mat(i) = new Array[(Int,Char)](8)
    for(j ← 0 to 7) {
      if(i == 0) mat(0)(j) = 0 → '✓'
      else mat(i)(j) = Int.MaxValue → '✓'
    }
  }

  //fill the matrix
  for{
    (row,i) ← board.zipWithIndex
    (col,j) ← row.zipWithIndex
  }{
    if(j > 0) {
      if(mat(i+1)(j-1)._1 > mat(i)(j)._1 + col(0)){
        mat(i+1)(j-1) = (mat(i)(j)._1 + col(0)) → '\\'
      }
    }
    if(mat(i+1)(j)._1 > mat(i)(j)._1 + col(1)){
      mat(i+1)(j) = (mat(i)(j)._1 + col(1)) → '|'
    }
    if(j < 7) {
      if(mat(i+1)(j+1)._1 > mat(i)(j)._1 + col(2)){
        mat(i+1)(j+1) = (mat(i)(j)._1 + col(2)) → '/'
      }
    }
  }

  //format solution as String
  val sol = new Array[String](8)
  var ((_,from),target) = mat(7).zipWithIndex.minBy(_._1._1)
  sol(0) = "#"*target+'X'+"#"*(7-target)
  for(i ← 6 to 0 by -1) {
    from = mat(i+1)(target)._2
    target = from match {
      case '\\' ⇒ target + 1
      case '|' ⇒ target
      case '/' ⇒ target - 1
    }
    sol(7-i) = "#"*target+from+"#"*(7-target)
  }
  sol.mkString("\n")
}

val input = Seq(
  Seq(Seq(1,1,1),Seq(1,1,1),Seq(0,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1)),
  Seq(Seq(1,1,1),Seq(1,0,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1)),
  Seq(Seq(1,1,1),Seq(1,1,0),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1)),
  Seq(Seq(1,1,1),Seq(1,1,1),Seq(1,1,0),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1)),
  Seq(Seq(1,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,0,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1)),
  Seq(Seq(1,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,0,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1)),
  Seq(Seq(1,1,1),Seq(1,1,1),Seq(1,1,1),Seq(0,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1),Seq(1,1,1))
)

println(solve(input))