First of all let me warn you that this method completely takes away the fun out of solving any of the jigsaw puzzles in this game, so I highly recommend you do this only for the really difficult 400 pieces hard, very hard and extreme levels.

The method is simple - Open the 400 pieces level and collect ALL the puzzle pieces from the sides and place them in the center of the board, on top of each other.



I have collected the edges and placed them at their correct places in the above image, but you can place even the edge pieces in the center as well, I just did it because of force of habit.

Once all the pieces are on top of each other, simply take the top piece and move it to any of the sides of the pieces below it. It WILL snap with an adjoining piece. Continue doing it until you get a large chunk of the joined pieces.



The reason I placed the stack in the center of the board is so that I can build a maximum possible size of snapped pieces, because once the pieces snap, you cannot move it outside the board.

Keep snapping them. The best way to get the largest possible size is to make a rectangle shape. It will also be even easier if you kept the 4 corner pieces separately and start snapping them using those 4 corner pieces.



Once further pieces cannot be added because of board boundary restriction, you can either look for the correct place to put the joined pieces, or simply toss them at the side, and then repeat the same process with the next piece in the center.

In no time, you will complete the puzzle!





Time taken to stack all pieces = 20 minutes
Time taken to snap all pieces < 5 minutes

One last tip - Always deactivate the box at the bottom in the "settings" because you will get two extra achievements if you complete all 400 pieces puzzles without using the box. Deactivate it because it is quite easy to place a piece in the box by mistake, which will prevent you from getting those two achievements, and later you'll have no idea which are the levels you used the box to solve.

Hope this was helpful.