input: 
  def is_palindrome(s: str) -> bool:
      """Determine if a given string is a palindrome.
      >>> is_palindrome("racecar")
      True
      >>> is_palindrome("hello")
      False
      """
      s = s.lower()
      left = 0
      right = len(s) - 1
      
      while left < right:
          if s[left] != s[right]:
              return False
          left += 1
          right -= 1
      return True
  
output:     s = s.lower()
      left = 0
      right = len(s) - 1
      
      while left < right:
          if s[left] != s[right]:
              return False
          left += 1
          right -= 1
      return True