In fact, pltrgyst, that's exactly how they made Cepheus.
They picked the simplest possible poker game:
- Holdem has more board cards / fewer player cards than others
- Heads-up has fewer situations than any higher number of players; you're always dealer, or not.
- Limit has fewer betting situation - check, bet, raise, fold. Never amounts. And there's no actual bankrolls; it's running scores, so all-in does not happen.
Then they wrote algorithms that remember each outcome for each possible situation (situation meaning each possible order of cards and betting order from start to finish), and figures the average result... it learns, through exposure, what decisions lead to the best outcomes.
And to give it that exposure - the chance to see all those situation - it played every deal against itself over and over. It played the equivalent of a billion billion hands against itself. It was never told what decisions were right - just that coming out ahead, on average, is better. It figured the rest out. It tried everything, lots of times, and saw what made for the best result in a given situation.
The total "strategy" is pre-calculated and saved on disk - i.e., how to play in every exact situation, including what percentage of the time to take each action (what percentage of the time to fold, call, and raise in a given situation). When I say "every situation," I mean, every situation - given these two hold cards in dealer position, with those four cards on the board, and this exact betting progression for preflop, and flop, and so far in the turn, Cepheus will now fold/call/raise this percentage of the time.
The total strategy, saved on disk, takes 12 terabytes of space, compressed. No pictures; all text and numbers. Crazy stuff... but remember, this was for the simplest stakes in the simplest player count in the simplest type of poker.