As long as the three sides are all different and it doesn't matter which order you select the sides in you can use a neat little addition trick:
Give each side an instance variable "value".
For each side assign "value" an increasing power of two e.g.
sideA = 1
sideB = 2
sideC = 4
sideD = 8
sideE = 16
Create a global called "AITotal".
Assign AITotal the sum of "value" for the three selected AI sides. This value will always be unique for each different combination of sides.
Create a global called "PlayerTotal".
Assign PlayerTotal the sum of "value" for the three player selected sides.
If AITotal is equal to PlayerTotal then the player has selected the same sides.
In fact I think this might work even if you have duplicates of the sides in the choice of three.