short deck evaluation

[travisstaloch]

Hello. I'm attempting to add support for short deck poker (9 rank deck 6-A rather than 13 rank 2-A). Right now I'm stuck trying to generate flush_sd and nonflush_sd look up tables (LUTs). I believe creating separate LUTs for this game is necessary because a flush beats a full house and A6789 is a straight in short deck. Would you agree that this is the best course? If so, can you recommend a strategy for creating these LUTs? I'm planning to submit a PR if i can figure out how to get this working.

I have calculated the number of distinct hands possible for each category as:

straight_flush:6,
four_kind: 72,
full_house:72,
flush:120,
straight:6,
three_kind:252,
two_pair:252,
one_pair:504,
high_card:120

Which gives these offsets:

6,78,150,270,276,528,780,1284,1404

I'm using the existing evaluate_5_cards method to find the correct rank/category. But I'm not sure how to construct the rest of the rank. Do you have any suggestions?

[HenryRLee]

Hi, @travisstaloch. If you allow some space in the value distribution (i.e. some value has no matching short deck poker hand), there is a much easier solution.

This is the standard deck 5-card hand distribution, with Full House better than Flush.

Hand Value	Distinct	Offset
Straight Flush	10	0
Four of a Kind	156	10
Full House	156	166
Flush	1277	322
Straight	10	1599
Three of a Kind	858	1609
Two Pair	858	2467
One Pair	2860	3325
High Card	1277	6185
		7462

We can turn that distribution into the following, so that Flush beats Full House:

Hand Value	Distinct	Offset
Straight Flush	10	0
Four of a Kind	156	10
Flush	1277	166
Full House	156	1443
Straight	10	1599
Three of a Kind	858	1609
Two Pair	858	2467
One Pair	2860	3325
High Card	1277	6185
		7462

Basically what you need to do is: after getting the value from evaluate_5_cards, if the value falls between 166 and 321 inclusively (which is a Full House), add an offset 1277 (subtract 166 from 1443) to the value. Else if the value is between 322 and 1598 inclusively (which is a Flush), add an offset -156 (subtract 322 from 166) to the value.

Now, we need to solve the edge case: the A 9 8 7 6 hand. Note that it can be a Straight or a Straight Flush. According to the 7426 table, the value of a suited A 9 8 7 6 hand is 747. Once you find out the value is 747 (before the flush/full house adjustment), adjust it to be 6. Similarly, once you get the value 6610 (the unsuited A 9 8 7 6), adjust it to be 1605.

[travisstaloch]

Thanks so much for the advice. I'll be working on this soon. Sounds fairly easy as you described. I think I need to adjust the card ids I'm using so that 2 => 6 and T => A before evaluating so that the ranks will begin at the category beginning. Will let you know.