input: Write a function to check if a given string is a palindrome. Convert the string to lowercase to handle case insensitivity, and then compare characters from the beginning and end moving towards the center. If all characters match, return True; otherwise, return False. If the string is empty, return True.
  assert is_palindrome("racecar")==True
  assert is_palindrome("hello")==False
  assert is_palindrome("A man a plan a canal Panama")==True
  assert is_palindrome("No lemon no melon")==True
  assert is_palindrome("")==True
output: def is_palindrome(s):
      s = s.lower().replace(" ", "")
      return s == s[::-1]