P = prize N = no prize X = opened non-prize door Combinations: PNN NPN NNP Let's say you choose door 1 One of the non-prize doors opens You will be left with combinations: PNX or PXN (this is not two combinations; it's the same combination with a different non-prize door opened) NPX NXP Because you don't have the option of choosing door X, you end up with two winning scenarios and one losing scenario. This is no different to being allowed to choose both of the other two doors instead of a non-prize door being opened: PNN NPN NNP You still have two winning combinations out of three.
i still have the application (not the code though) if anyone wants to try it just reply to the thread and ill update the link