input: Write a function to determine if a string s has matching parentheses. If the string contains only matching parentheses return True else return False.
  assert matching_paren("()")==True
  assert matching_paren("())")==False
  assert matching_paren("(())")==True
  assert matching_paren("(()")==False
  assert matching_paren("")==True
output: def matching_paren(s):
      count = 0
      for char in s:
          if char == '(':
              count += 1
          elif char == ')':
              count -= 1
          if count < 0:
              return False
      return count == 0