compiler/testcases/queens.tig

   1 /* A program to solve the 8-queens problem */
   2
   3 let
   4   var N := 8
   5
   6   type intArray = array of int
   7
   8   var row := intArray [ N ] of 0
   9   var col := intArray [ N ] of 0
  10   var diag1 := intArray [N+N-1] of 0
  11   var diag2 := intArray [N+N-1] of 0
  12
  13   function printboard() = (
  14     for i := 0 to N-1 do (
  15       for j := 0 to N-1 do print(if col[i]=j then " O" else " .");
  16       print("\n")
  17     );
  18     print("\n")
  19   )
  20
  21   function try(c:int) = (
  22     /*  for i:= 0 to c do print("."); print("\n"); flush();*/
  23     if c=N
  24     then printboard()
  25     else
  26       for r := 0 to N-1
  27       do
  28         if row[r]=0 & diag1[r+c]=0 & diag2[r+7-c]=0
  29         then (
  30           row[r]       := 1;
  31           diag1[r+c]   := 1;
  32           diag2[r+7-c] := 1;
  33           col[c]       := r;
  34           try(c+1);
  35           row[r]       := 0;
  36           diag1[r+c]   := 0;
  37           diag2[r+7-c] := 0
  38         )
  39   )
  40 in
  41   try(0)
  42 end