Bite 77. New places to travel to

You want to find people who have as much exposure to different cultures as yourself.

Complete the uncommon_cities helper that takes the cities you have visited (my_cities) and the cities the other person has visited (other_cities) and returns the number of cities that both sequences do NOT have in common.

So given [A B C] and [B C D] it should return 2 because only A and D are different.

You can loop through both sequences but maybe there is a more concise way to do it?