In this Kata, you will be given an array of integers whose elements have both a negative and a positive value, except for one integer that is either only negative or only positive. Your task will be to find that integer.
Examples:
[1, -1, 2, -2, 3] => 3
3 has no matching negative appearance
[-3, 1, 2, 3, -1, -4, -2] => -4
-4 has no matching positive appearance
[1, -1, 2, -2, 3, 3] => 3
(the only-positive or only-negative integer may appear more than once)