input: Write a python function to check for valid parentheses in a string.
  assert isValid('[[{{}}]]') == True
  assert isValid('[[{()}]]') == True
  assert isValid('[[{(})]]') == False
  assert isValid('') == True
output: def isValid(s: str) -> bool:
      stack = []
      mapping = {')': '(', '}': '{', ']': '['}
      
      for char in s:
          if char in mapping:
              top_element = stack.pop() if stack else '#'
              if mapping[char] != top_element:
                  return False
          else:
              stack.append(char)
      
      return not stack