input: Write a function to find the most common elements in an array of integers. If there are multiple elements with the same highest frequency, return all such elements.
  def most_common(nums):
      counts = {}
      for num in nums:
          if num not in counts:
              counts[num] = 0
          counts[num] += 1
      max_count = max(counts.values())
      return [num for num, count in counts.items() if count == max_count]
  
  assert most_common([3, 4, 1, 2, 5, 3, 3])==[3]
  assert most_common([1, 2, 3, 4, 5, 1, 2, 3])==[1, 2, 3]
  assert most_common([])==[]
  assert most_common([1, 1, 2, 2, 3, 3, 4, 4])==[1, 2, 3, 4]
output: def most_common(nums):
      counts = {}
      for num in nums:
          if num not in counts:
              counts[num] = 0
          counts[num] += 1
      max_count = max(counts.values(), default=0)
      return [num for num, count in counts.items() if count == max_count]