Oz Constraint logic programming : 2016-03-21 Exercice 2 (Queens)

queens.oz

% Author: Pierre Dargham
% Author-URI : https://github.com/pierre-dargham

declare

fun {Board Width}
   
   proc {Script Solution}

      % Board and Cells

      Size = Width*Width
      Cells = {FD.tuple cells Size 0#2}
      Count = {FD.int 0#Size}
      Whites
      Blacks
      
      % Board mathematics

      Up = ~Width
      Right = 1
      Bottom = Width
      Left = ~1
      Offsets = [Up Up+Right Right Right+Bottom Bottom Bottom+Left Left Left+Up]

      % Utils
      
      fun {IsWhite Cell}
	 Cell == 1
      end

      fun {IsBlack Cell}
	 Cell == 2
      end

      fun {NextCell I Offset}
	 J = I + Offset
      in
	 if J < 1 then 0
	 elseif J > Size then 0
	 elseif Cells.J == 0 then {NextCell J Offset}
	 else Cells.J
	 end
      end
      
   in
      % Solution
      Solution = solution(board: Cells count: Count)

      % Distribution
      {FD.distribute ff Cells}

      % Whites and blacks
      Whites = {Record.filter Cells IsWhite}
      Blacks = {Record.filter Cells IsBlack}

      % Propagators (blacks and whites sizes)
      Count =: {Record.width Whites} + {Record.width Blacks}
      {Record.width Whites} =: {Record.width Blacks}

      % Propagators (peace) - One by one :
      %{Record.forAllInd Whites proc {$ I C} {NextCell I Up} \=: 2 end}
      %{Record.forAllInd Whites proc {$ I C} {NextCell I Up+Right} \=: 2 end}
      %{Record.forAllInd Whites proc {$ I C} {NextCell I Right} \=: 2 end}
      %{Record.forAllInd Whites proc {$ I C} {NextCell I Right+Bottom} \=: 2 end}
      %{Record.forAllInd Whites proc {$ I C} {NextCell I Bottom} \=: 2 end}
      %{Record.forAllInd Whites proc {$ I C} {NextCell I Bottom+Left} \=: 2 end}
      %{Record.forAllInd Whites proc {$ I C} {NextCell I Left} \=: 2 end}
      %{Record.forAllInd Whites proc {$ I C} {NextCell I Left+Up} \=: 2 end}

      % Propagators (peace) - All together :
      %{Record.forAllInd Whites proc {$ I C} {List.forAll Offsets proc {$ Offset} {NextCell I Offset} \=: 2 end} end}
   end

   % Sort function
   proc {Order A B}
      A.count <: B.count
   end
in
   % Return the best solution
   {SearchBest Script Order}
end

% Example 1
{Browse {Board 3}}