Programming Project #2: Calculating probabilities in poker

Due Wednesday, March 25, 2009


In this project, you are a player in a game of Texas hold'em. The cards have been dealt, and you want to know the odds that no other player at the table has a better hand. To do this, you're going to need to know (a) how to play poker, including specifically (b) how to compare two poker hands, and (c) how to enumerate all possible hands your competitors might have in order to compute your odds of winning.

Texas Hold'em

For the purposes of this assignment, here's how the game works. (We're ignoring the rounds of betting and dealing.) There are five cards revealed on the table (the "community" cards). There are two cards in your hand (the "hole" cards). That's seven, from which you will choose the optimal five-card hand. (A poker hand is always five cards.) Each other player uses those same community cards plus the two cards they have in their own hand (hidden from you). Whoever can produce the best five-card hand wins.

Note: everyone here knows how to find the best five-card hand, so this will not be a game of strategy. You just want to know, given the cards available, how likely your hand is to win.

Poker hands

Wikipedia's article on poker hands is a good place to learn about hands and their ranking. (Also useful: this summary and Wikipedia on Texas hold'em.)

Here's a brief version of how to compare two five-card poker hands.

Other players

They work how you would think. You can see 7 cards. There are 45 other cards in the deck, and each of the b other players has 2 of them. For example, if there are two other players, you could look at 45C2 * 43C2 configurations.

Notice that in this example, if player 1 has cards {1, 2} and player 2 has {3, 4}, it's all the same to you as if player 1 had {3, 4} and player 2 had {1, 2}. We don't need to distinguish who has what. So above, we actually double counted the configurations. But it's tricky to not double count; it would work differently for each b. It's okay not to worry about that here; as long as we're overcounting each configuration equally many times, the probabilities will come out right. Extra credit if you find and implement a solution that reduces the overcounting of the method shown above.


You are provided a code base that knows a few things about poker.

The second (and larger) part of the assignment is to implement Deal.computeOdds() -- iterate through possible hands of the other players to compute the probability that you have the highest hand (where a tie != highest). The input to the program will be your cards, the community cards, and the number of other players. The output will be your probability of winning.

For computeOdds(), you will need to write a helper function that takes a set and shifts it over: mapToAvailableCards(). For example, if 7 cards have already been dealt--say, the Ace through 7 of spades--and we are choosing two more from the remaining pool of 45, the function needs to map from the range 1-45 to the 45 available card values.

In general, add any extra methods you find helpful, but be cautious about changing the existing code unless you're sure you know what you're doing.


The 5 java files needed for this assignment are in a folder called proj2 in the cs240 directory of the edlab machines. To get to it, use this link to the ftp server, or see the edlab main page for other ways to connect.

While you're there, you can also download a working version of proj1, in case you need one. As we've mentioned, this code could help you solve some problems on HW#2 if you don't trust your own code.

Submit the 5 completed java files to the cs240 folder of your own home directory by midnight on Wednesday, March 25, 2009.