count successive occurrences of number in Prolog

Question

Hello I am trying to make a program in Prolog that given a list it counts the occurrences of each successive element in the list as follows:

count(1,[1,1,1,2,2,2         


        

Answer 1

Why you are stating a relation between two lists with a predicate having 4 arguments ? Let's try to proceed step by step.

An empty list gives an empty list, an element counted gets incremented, otherwise, start counting...

count([],[]).
count([X|T],[[X,C1]|R]) :- count(T,[[X,C]|R]), !, C1 is C+1.
count([X|T],[[X,1]|R]) :- count(T,R).

?- count([1,1,1,2,2,2,3,1,1],R).
R = [[1, 3], [2, 3], [3, 1], [1, 2]].

so easy (of course, assuming X=[ [1,3],[2,3],[1,3][1,2] ] it's a typo ...)