hj_queens.tig

/* A program to solve the 8-queens problem */

let
    var N := 8

    type intArray = array of int

    var row := intArray [ N ] of 0
    var col := intArray [ N ] of 0
    var diag1 := intArray [N+N-1] of 0
    var diag2 := intArray [N+N-1] of 0

    function printboard() =
     (
          for i := 0 to N - 1
	     do (for j := 0 to N - 1
	          do print(if col[i]=j then "O" else ".");
               print("\n")
	     );
         print("===========\n")
     )

     function try(c:int) = 
     ( 
          if c=N
          then printboard()
          else for r := 0 to N - 1
          do 
          (
               if row[r]=0 & diag1[r+c]=0 & diag2[r+7-c]=0
                    then (row[r]:=1; diag1[r+c]:=1; diag2[r+7-c]:=1;
                    col[c]:=r;
                         try(c+1);
                    row[r]:=0; diag1[r+c]:=0; diag2[r+7-c]:=0)
          )

     )
 in try(0)
end