Uncommon numbers of two arrays

Write a function uncommonNumbers(a, b) that returns the numbers that are in exactly one of two arrays.

• a and b are arrays of integers, zero and negative numbers too. They can be empty and can have repeated numbers.
• A number that is in both arrays (in their intersection) is not in the result.
• Every number is in the result once, even if it is a duplicate inside its array: [1, 1, 2] and [2, 3] give [1, 3].
• Order: first the numbers from a in the order of their first occurrence in a, then the numbers from b in the same way. Do not sort the result.
• Return a new array. If there are no such numbers, return an empty array.

A set of each array helps you check quickly if a number is in it.