I solved using the python build in dictionary, more code but more easy for beginers:

def countTriplets(arr, r):
        # initialize the dictionaries
        r2 = {}
        r3 = {}
        count = 0

        # loop throgh the arr itens
        for k in arr:
                # if k in r3 indicates the triplet already completed,
                # the count need be incremented
                if k in r3:
                        count += r3[k]

                # if k in r2, it is the secound number of the triplet,
                # your successor (third element k*r) need be added or incremented in the r3 dict
                # because is a potencial triplet 
                if k in r2:
                        if k*r in r3:
                                r3[k*r] += r2[k]
                        else:
                                r3[k*r] = r2[k]

                # else, k is the first element of the triplet, so,
                # your seccessor (secound element k*r) need be added or incremented in the r2 dict
                # because is a potencial triplet
                if k*r in r2:
                        r2[k*r] += 1
                else:
                        r2[k*r] = 1

        return count