diff -r 9b5165b8a762 -r 0587ef444547 progs/knight2.scala
--- a/progs/knight2.scala	Sat Mar 11 23:12:49 2023 +0000
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,81 +0,0 @@
-// Part 2 about finding a single tour for a board
-//================================================
-
-type Pos = (Int, Int)    // a position on a chessboard 
-type Path = List[Pos]    // a path...a list of positions
-
-
-// for measuring time
-def time_needed[T](n: Int, code: => T) : T = {
-  val start = System.nanoTime()
-  for (i <- 0 until n) code
-  val result = code
-  val end = System.nanoTime()
-  println("Time needed: " + (end - start) / 1.0e9 + " secs.")
-  result
-}
-
-
-def print_board(dim: Int, path: Path): Unit = {
-  println
-  for (i <- 0 until dim) {
-    for (j <- 0 until dim) {
-      print(f"${path.reverse.indexOf((i, j))}%3.0f ")
-    }
-    println
-  } 
-}
-
-def add_pair(x: Pos)(y: Pos): Pos = 
-  (x._1 + y._1, x._2 + y._2)
-
-def is_legal(dim: Int, path: Path)(x: Pos): Boolean = 
-  0 <= x._1 && 0 <= x._2 && x._1 < dim && x._2 < dim && !path.contains(x)
-
-def moves(x: Pos): List[Pos] = 
-  List(( 1,  2),( 2,  1),( 2, -1),( 1, -2),
-       (-1, -2),(-2, -1),(-2,  1),(-1,  2)).map(add_pair(x))
-
-def legal_moves(dim: Int, path: Path, x: Pos): List[Pos] = 
-  moves(x).filter(is_legal(dim, path))
-
-
-def first(xs: List[Pos], f: Pos => Option[Path]): Option[Path] = xs match {
-  case Nil => None
-  case x::xs => {
-    val result = f(x)
-    if (result.isDefined) result else first(xs, f)
-  }
-}
-
-first(List((1, 0),(2, 0),(3, 0),(4, 0)), (x => if (x._1 > 3) Some(List(x)) else None))
-first(List((1, 0),(2, 0),(3, 0)), (x => if (x._1 > 3) Some(List(x)) else None))
-
-
-
-def first_tour(dim: Int, path: Path): Option[Path] = {
-  if (path.length == dim * dim) Some(path)
-  else
-    first(legal_moves(dim, path, path.head), (x: Pos) => first_tour(dim, x::path))
-}
-
-/*
-for (dim <- 1 to 8) {
-  val t = first_tour(dim, List((0, 0)))
-  println(s"${dim} x ${dim} " + (if (t == None) "" else { print_board(dim, t.get) ; "" }))
-}
-*/
-
-// 15 secs for 8 x 8
-val ts1 = time_needed(0,first_tour(8, List((0, 0))).get)
-
-// no result for 4 x 4
-val ts2 = time_needed(0, first_tour(4, List((0, 0))))
-
-// 0.3 secs for 6 x 6
-val ts3 = time_needed(0, first_tour(6, List((0, 0))))
-
-// 15 secs for 8 x 8
-time_needed(0, print_board(8, first_tour(8, List((0, 0))).get))
-
-