[Yawkey]

I'm not sure that your second solution is straight forward, why randomly generate 52 different cards when all you need is 15-25. If I were programming it I would opt for the one card at a time method. I don't think we can assume any poker room does it either way, and some may in fact generate the entire deck for each hand. Every different poker room has it's own algorithm, and they are trade secrets as releasing to the public could certainly damage the card rooms integrity.

The other thing that you may want to think about is seed selection. I would be very suprised if the poker rooms selected a new seed for every card that is dealt, maybe not even every hand. This means they are relying on the complexity of their algorithm to keep players guessing what card is to come next. In theory with a large enough sample size, one could eventually determine the algorithm used at their favorite online poker room (you may have more success at a blackjack table where you can see every card dealt, if you never hit). I believe there is at least one known instance where some people did figure out a card rooms algorithm and made a lot of money from it, I can't think of it off the top of my head but I will look it up, and report back.