--- a/progs/knight1.scala	Tue Nov 20 13:42:32 2018 +0000
+++ b/progs/knight1.scala	Tue Nov 20 14:31:14 2018 +0000
@@ -4,33 +4,95 @@
 type Pos = (Int, Int)    // a position on a chessboard 
 type Path = List[Pos]    // a path...a list of positions
 
-//(1a) Complete the function that tests whether the position 
-// is inside the board and not yet element in the path.
+def print_board(dim: Int, path: Path): Unit = {
+  println
+  for (i <- 0 until dim) {
+    for (j <- 0 until dim) {
+      print(f"${path.reverse.indexOf((j, dim - i - 1))}%3.0f ")
+    }
+    println
+  } 
+}
 
-def is_legal(dim: Int, path: Path)(x: Pos): Boolean = ...
+
+// 1 mark
+
+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)
+
+assert(is_legal(8, Nil)((3,4)) == true)
+assert(is_legal(8, List((4,1), (1,0)))((4,1)) == false)
+assert(is_legal(2, Nil)((0,0)) == true)
 
 
-//(1b) Complete the function that calculates for a position 
-// all legal onward moves that are not already in the path. 
-// The moves should be ordered in a "clockwise" order.
- 
-def legal_moves(dim: Int, path: Path, x: Pos): List[Pos] = ...
+def add_pair(x: Pos)(y: Pos): Pos = 
+  (x._1 + y._1, x._2 + y._2)
+
+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))
+
+// 1 mark
+
+def legal_moves(dim: Int, path: Path, x: Pos): List[Pos] = 
+  moves(x).filter(is_legal(dim, path))
 
-//assert(legal_moves(8, Nil, (2,2)) == 
-//  List((3,4), (4,3), (4,1), (3,0), (1,0), (0,1), (0,3), (1,4)))
-//assert(legal_moves(8, Nil, (7,7)) == List((6,5), (5,6)))
-//assert(legal_moves(8, List((4,1), (1,0)), (2,2)) == 
-//  List((3,4), (4,3), (3,0), (0,1), (0,3), (1,4)))
-//assert(legal_moves(8, List((6,6)), (7,7)) == List((6,5), (5,6)))
+assert(legal_moves(8, Nil, (2,2)) == 
+  List((3,4), (4,3), (4,1), (3,0), (1,0), (0,1), (0,3), (1,4)))
+assert(legal_moves(8, Nil, (7,7)) == List((6,5), (5,6)))
+assert(legal_moves(8, List((4,1), (1,0)), (2,2)) == 
+  List((3,4), (4,3), (3,0), (0,1), (0,3), (1,4)))
+assert(legal_moves(8, List((6,6)), (7,7)) == List((6,5), (5,6)))
+assert(legal_moves(1, Nil, (0,0)) == List())
+assert(legal_moves(2, Nil, (0,0)) == List())
+assert(legal_moves(3, Nil, (0,0)) == List((1,2), (2,1)))
+
+// 2 marks
+
+def count_tours(dim: Int, path: Path): Int = {
+  if (path.length == dim * dim) 1
+  else 
+    (for (x <- legal_moves(dim, path, path.head)) yield count_tours(dim, x::path)).sum
+}
+
+def enum_tours(dim: Int, path: Path): List[Path] = {
+  if (path.length == dim * dim) List(path)
+  else 
+    (for (x <- legal_moves(dim, path, path.head)) yield enum_tours(dim, x::path)).flatten
+}
+
+// as far as tasks go
 
 
-//(1c) Complete the two recursive functions below. 
-// They exhaustively search for open tours starting from the 
-// given path. The first function counts all possible open tours, 
-// and the second collects all open tours in a list of paths.
 
-def count_tours(dim: Int, path: Path): Int = ...
+def count_all_tours(dim: Int) = {
+  for (i <- (0 until dim).toList; 
+       j <- (0 until dim).toList) yield count_tours(dim, List((i, j)))
+}
 
-def enum_tours(dim: Int, path: Path): List[Path] = ...
+def enum_all_tours(dim: Int): List[Path] = {
+  (for (i <- (0 until dim).toList; 
+        j <- (0 until dim).toList) yield enum_tours(dim, List((i, j)))).flatten
+}
 
 
+println("Number of tours starting from (0, 0)")
+
+for (dim <- 1 to 5) {
+  println(s"${dim} x ${dim} " + count_tours(dim, List((0, 0))))
+}
+
+for (dim <- 1 to 5) {
+  println(s"${dim} x ${dim} " + count_all_tours(dim))
+}
+
+for (dim <- 1 to 5) {
+  val ts = enum_tours(dim, List((0, 0)))
+  println(s"${dim} x ${dim} ")   
+  if (ts != Nil) {
+    print_board(dim, ts.head)
+    println(ts.head)
+  }
+}
+
+