input: Write a python function to generate an array of unique random numbers.
  assert len(random_array(10)) == 10 and len(set(random_array(10))) == 10
  assert len(random_array(5)) == 5 and len(set(random_array(5))) == 5
  assert len(random_array(0)) == 0
output: import random
  
  def random_array(n):
      return random.sample(range(n * 2), n)