input: Write a function to find the number of occurrences of an element x in a list y. If the list is empty, return 0.
  def count_x(x, y):
      count = 0
      for i in y:
          if i == x:
              count += 1
      return count
  
  assert count_x(2, [3, 5, 2, 7, 4, 3, 2])==2
  assert count_x(3, [1, 2, 3, 3, 4, 3])==3
  assert count_x(5, [1, 2, 4, 5, 5, 6, 6])==2
  assert count_x(7, [1, 2, 3, 4, 5, 6])==0
  assert count_x(1, [])==0
output: def count_x(x, y):
      count = 0
      for i in y:
          if i == x:
              count += 1
      return count