I have a deck of 52 poker cards represented as array of int – [0, 1, ... 51].
There are 2.598.960 possible combinations of 5 cards. I can generate all combinations like this:
#id #combination
0 - 0, 1, 2, 3, 4
1 - 0, 1, 2, 3, 5
2 - 0, 1, 2, 3, 6
...omitted data..
2598957 - 46, 47, 49, 50, 51
2598958 - 46, 48, 49, 50, 51
2598959 - 47, 48, 49, 50, 51
How I can effectively find #id for given #combination and #combination for given #id?
3
For the first card you have 52 options for the second you have 51 and so on. You need to encode a sequence c1, c2, c3, c4 and c5 where there are 52, 51, 50 ,49, 48 options resp.
You can adjust the numbers by counting how many of the previous numbers are smaller: a5 = c5 - sum(x < c5 for x in [c1, c2, c3, c4])
you can simply encode it as a single integer output =(((a1*51 + a2)*50 + a3)*49 + a4)*48 + a5.
you can extract it by using the modulo operation and integer divide.
int input = //...
a5 = input%48;
input/=48;
a4 = input%49;
input/=49;
a3 = input%50;
input/=50;
a2 = input%51;
input/=51;
a1 = input;
And then the reverse operation is needed to adjust them all back into the range [0..52).
6