input: Write a function to determine if a given string is a palindrome. The function should return True if the string is a palindrome, otherwise it should return False. If the input string is empty, the function should return True.
  
  def is_palindrome(s):
      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
  
  assert is_palindrome("racecar")==True
  assert is_palindrome("madam")==True
  assert is_palindrome("hello")==False
  assert is_palindrome("Able was I ere I saw Elba")==True
  assert is_palindrome("")==True
output: def is_palindrome(s):
      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