How to count different players in a 2d array in Prolog

for example I have a 2d array like this in prolog: [3 ,2 ,2 ,3 ,3]. [3 ,1 ,3 ,1 ,3]. [1 ,3 ,3 ,3 ,3]. [2 ,1 ,1 ,1 ,1]. [3 ,2 ,3 ,3 ,3]. the number of player will be 3.

If 2d array like this: [2 ,1] [1 ,1] [2 ,1] [2 ,1]

number of player will be 2. I need to solve this problem in Prolog. Thanks for any help.