Easy or Difficult ?

It all depends on the Size and Distribution of digits. Size 3×3 is fairly easy to solve, but sometimes Distribution of numbers makes it little more harder. When the Size grows, from sizes 4×4, 5×5, classic 6×6 to 25×25 for example, difficulties grow but mainly because of time needed to find correct place for tiles. We cannot categorize Dominosa similar to Sudoku, from Easy to Diabolic. I think that Dominosa is much more “democratic“ puzzle than Sudoku (and many more so called Japanese puzzles like Kakuro). What I mean is that the distance between easy and hard puzzle is very small. More on this later.