Clever, but it seems like you're still encoding states separately. For an undo/redo stack, you can probably do much better spacewise with some sort of delta-enc

Clever, but it seems like you're still encoding states separately. For an undo/redo stack, you can probably do much better spacewise with some sort of delta-encoding, either by explicitly storing the changes made to the grid (or more accurately, the inverse of changes, so you can undo them) or by comparing the new state with the last one whenever saveUndo() is called and storing only the difference.