{$MODE OBJFPC} { -*- delphi -*- }
{$INCLUDE settings.inc}
program sudoku;
uses
   {$IFDEF DEBUG} debug, {$ENDIF}
   sysutils;

const
   SideSize = 9;
   BoxSize = 3;

type
   TDigit = 1..9;
   TDigits = set of TDigit;
   TPosition = 0..SideSize-1;
   TGrid = array[TPosition, TPosition] of TDigits;
   TSolutionCount = (scInvalid, scUnique, scAmbiguous);

function BlankGrid(): TGrid;
var
   X, Y: Integer;
begin
   for X := 0 to SideSize - 1 do
   begin
      for Y := 0 to SideSize - 1 do
      begin
         Result[X, Y] := [Low(TDigit) .. High(TDigit)];
      end;
   end;
end;

function PlaceDigit(Grid: TGrid; const Digit: TDigit; const DigitX, DigitY: TPosition): TGrid;
var
   X, Y, BoxX, BoxY: Integer;
begin
   Assert(Digit in Grid[DigitX, DigitY]);
   Assert(Grid[DigitX, DigitY] - [Digit] <> []);
   // remove everything else in this cell
   Grid[DigitX, DigitY] := [Digit];
   // remove from row 
   for X := 0 to SideSize - 1 do
   begin
      if (X <> DigitX) then
      begin
         Exclude(Grid[X, DigitY], Digit);
      end;
   end;
   // remove from column
   for Y := 0 to SideSize - 1 do
   begin
      if (Y <> DigitY) then
      begin
         Exclude(Grid[DigitX, Y], Digit);
      end;
   end;
   // remove from box
   BoxX := (DigitX mod BoxSize) * BoxSize; // $R-
   BoxY := (DigitY mod BoxSize) * BoxSize; // $R-
   for X := BoxY to BoxY + BoxSize - 1 do // $R-
   begin
      for Y := BoxX to BoxX + BoxSize - 1 do // $R-
      begin
         if ((X <> DigitX) and (Y <> DigitY)) then
         begin
            Exclude(Grid[X, Y], Digit);
         end;
      end;
   end;
   Result := Grid;
end;

function Solve(Grid: TGrid): TSolutionCount;
begin
   
end;

function PlaceDigit(Grid: TGrid): TGrid;
begin
end;

procedure WriteGrid(Grid: TGrid);
var
   X, Y: Integer;
begin
   for Y := 0 to SideSize - 1 do
   begin
      for X := 0 to SideSize - 1 do
      begin
         if (Grid[X, Y]
         Write(Grid[X, Y]:3);
      end;
      Writeln();
   end;
end; 

begin
   Writeln(BlankGrid());
end.