input: Write a function to check whether an array has an even or odd number of elements. If the array has an even number of elements, return True; otherwise, return False. If the array is empty, return True.
  assert check_elements_parity([])==True
  assert check_elements_parity([1, 2, 3, 4])==True
  assert check_elements_parity([1, 2, 3])==False
  assert check_elements_parity([1])==False
output: def check_elements_parity(arr):
      return len(arr) % 2 == 0