Championship Freecell
Prediction
Probably the three most interesting new aspects of Championship Freecell are the ability to play with different numbers of free cells, the competition system, and the prediction system incorporated into the application. The original Freecell application would stop the game when no more moves were left, but our prediction system uses a much more powerful algorithm to determine when the game you're playing is no longer winnable. Even if you still have many possible moves, the prediction algorithm will detect if you are in an unwinnable situation and warn you. Although technically the algorithm is a "heuristic", meaning it might miss detecting an unwinnable game in some circumstances, we have never seen it fail when turned to its most sensitive setting (via the Prediction Menu in the Championship Freecell application).
In fact, this new algorithm uncovers something very interesting about Freecell. We've discovered that the algorithm is useful not so much for the warnings it does give as for the ones it does not give. It often does not detect an unwinnable game, even when you're certain the game is lost. In all cases where this has happened, with the algorithm turned to its highest setting, we've discovered to our surprise that the algorithm was right, and in fact the game was winnable after all. By doing some random sampling with the help of the prediction algorithm, we've found that about 12% of games are winnable with just one free cell, around 80% are winnable with two free cells, and almost all are winnable with just three free cells. The solutions are by no means obvious, but they do exist.
To summarize, if you have the prediction algorithm set to its highest level, and it doesn't warn you, then the game is almost certainly winnable no matter how impossible it looks. If it does warn you, you won't win unless you undo at least one move.
Because the prediction algorithm is so powerful, we've had to place a limit on another Championship Freecell feature to keep the challenge in the game. Championship Freecell does have an "undo move" feature, like many other implementations of the game. Theoretically, you could beat your way to a solution by simply making moves until the prediction algorithm warns you, then undoing a move and trying alternatives, effectively letting the prediction algorithm guide you to a solution. To prevent this, the free version of the Championship Freecell application turns off the undo feature after your second "lost-game" warning from the prediction algorithm. (Gold Freecell turns off the undo after the fourth "lost-game" warning.)
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