7 Use Map Please

You are given a sequence of $N$ integers, $a = (a_1, a_2, ..., a_N)$. The elements of the sequence are not necessarily distinct. Let's define a sequence to be a **good sequence** if the frequency of each element in the sequence is exactly 1 i.e, all elements of the sequence are unique. For example of : $(1, 2, 3), (2, 6, 7), (3, 4), (6), (9)$ are good sequences while $(3, 4, 3), (6, 6, 9),