--- a/progs/knight3_sol.scala	Sat Mar 11 23:12:49 2023 +0000
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,99 +0,0 @@
-// Part 3 about finding a single tour using the Warnsdorf Rule
-//=============================================================
-
-
-type Pos = (Int, Int)
-type Path = List[Pos]
-
-def print_board(dim: Int, path: Path): Unit = {
-  println
-  for (i <- 0 until dim) {
-    for (j <- 0 until dim) {
-      print(f"${path.reverse.indexOf((i, j))}%3.0f ")
-    }
-    println
-  } 
-}
-
-def add_pair(x: Pos)(y: Pos): Pos = 
-  (x._1 + y._1, x._2 + y._2)
-
-def is_legal(dim: Int, path: Path)(x: Pos): Boolean = 
-  0 <= x._1 && 0 <= x._2 && x._1 < dim && x._2 < dim && !path.contains(x)
-
-def moves(x: Pos): List[Pos] = 
-  List(( 1,  2),( 2,  1),( 2, -1),( 1, -2),
-       (-1, -2),(-2, -1),(-2,  1),(-1,  2)).map(add_pair(x))
-
-def legal_moves(dim: Int, path: Path, x: Pos): List[Pos] = 
-  moves(x).filter(is_legal(dim, path))
-
-def ordered_moves(dim: Int, path: Path, x: Pos): List[Pos] = 
-  legal_moves(dim, path, x).sortBy((x) => legal_moves(dim, path, x).length)
-
-import scala.annotation.tailrec
-
-/*
-@tailrec
-def first(xs: List[Pos], f: Pos => Option[Path]): Option[Path] = xs match {
-  case Nil => None
-  case x::xs => {
-    val result = f(x)
-    if (result.isDefined) result else first(xs, f)
-  }
-}
-*/
-
-def first[A, B](xs: List[A], f: A => Option[B]): Option[B] =
-  xs.flatMap(f(_)).headOption
-
-
-def first_closed_tour_heuristics(dim: Int, path: Path): Option[Path] = {
-  if (path.length == dim * dim && moves(path.head).contains(path.last)) Some(path)
-  else
-    first(ordered_moves(dim, path, path.head), (x: Pos) => first_closed_tour_heuristics(dim, x::path))
-}
-
-/*
-for (dim <- 1 to 6) {
-  val t = first_closed_tour_heuristics(dim, List((dim / 2, dim / 2)))
-  println(s"${dim} x ${dim} closed: " + (if (t == None) "" else { print_board(dim, t.get) ; "" }))
-}
-*/
-
-//@tailrec
-def first_tour_heuristics(dim: Int, path: Path): Option[Path] = {
-
-  @tailrec
-  def aux(dim: Int, path: Path, moves: List[Position]): Option[Path 
-  if (path.length == dim * dim) Some(path)
-  else
-    moves match {
-      case Nil => None
-      case x::xs => {
-        val r = first_tour_heuristics(dim, x::path)
-        if (r.isDefined) Some(r) else aux(dim, path, xs)
-    }    
-  aux(dim, path, ordered_moves(dim, path, path.head)) 
-}
-
-
-/*
-def first_tour_heuristics(dim: Int, path: Path): Option[Path] = {
-  if (path.length == dim * dim) Some(path)
-  else
-    for (p <- ordered_moves(dim, path, path.head))
-      val r = first_tour_heuristics(dim, x::path)
-    //first(ordered_moves(dim, path, path.head), (x: Pos) => first_tour_heuristics(dim, x::path))
-    ordered_moves(dim, path, path.head).view.flatMap((x: Pos) => first_tour_heuristics(dim, x::path)).headOption
-}
-*/ 
-
-/*
-for (dim <- 1 to 50) {
-  val t = first_tour_heuristics(dim, List((dim / 2, dim / 2)))
-  println(s"${dim} x ${dim}: " + (if (t == None) "" else { print_board(dim, t.get) ; "" }))
-}
-*/
-
-print_board(50, first_tour_heuristics(50, (25,25)::Nil).get)