Number of solutions of a randomization

SystemVerilog
, ,
4

In reply to sharatk:

I was thinking of solving this exact example problem, but never made it past the mental exercise phase.

Assuming you have a class that models your sudoku puzzle, you’ll need an encapsulating class that contains two sudoku instances. In both instances you set the values of the fixed cells and turn rand_mode off on those cells. Then randomize one instance, which should generate a solution.

Then the encapsulating class provides a constraint to enforce the 2 instances are not identical. i.e.

class unique_solution;
  sodoku a = new;
  rand sodoku b = new;
  constraint {
    a.cell != b.cell;
  }
  function set( int x, y, val );
    a.cell[x][y] == val; a.cell[x][y].rand_mode(0);
    b.cell[x][y] == val; b.cell[x][y].rand_mode(0);
  endfunction

  function void solve();
    // set fixed cells
    set( 1, 4, 3 );
    set( 6, 8, 2 );
    ...
    // find a solution
    if ( a.randomize() ) begin
       $display(" found a solution ");
       if ( this.randomize() ) begin
         $display(" found another solution, first was not unique ");
       end
       else begin
         $display(" no other solution found, the first one was unique ");
       end
    end
    else begin
      $display(" your puzzle has no solution ");
    end
    
endclass

Now, how well solvers handle this could be another issue.

*edited