You are given an array of n unique integer numbers 0 <= x_i < 2 * n
Print all integers 0 <= x < 2 * n that are not present in this array.
Example:
find_missing([0]) = [1]
find_missing([0, 2, 4]) = [1, 3, 5] # because all numbers are [0, 1, 2, 3, 4, 5]
find_missing([]) = []
find_missing([0, 1, 4, 5]) = [2, 3, 6, 7] # because all numbers are [0, 1, 2, 3, 4, 5, 6, 7]
