input: Write a function to find the most common elements in an array of integers. The function should return a list of elements that appear most frequently in the given array. If multiple elements have the same highest frequency, they should all be included in the result. If the array is empty, the function should return an empty list.
  
  
  assert most_common([3, 4, 1, 2, 5, 3, 3])==[3]
  assert most_common([1, 1, 2, 2, 3, 3])==[1, 2, 3]
  assert most_common([1, 2, 3, 4, 5])==[1, 2, 3, 4, 5]
  assert most_common([])==[]
  
output: def most_common(arr):
      if not arr:
          return []
      freq = {}
      for num in arr:
          if num in freq:
              freq[num] += 1
          else:
              freq[num] = 1
      max_freq = max(freq.values())
      return [num for num, count in freq.items() if count == max_freq]