input: Write a python function to check if a string is a palindrome.
  assert is_palindrome("racecar") == True
  assert is_palindrome("hello") == False
  assert is_palindrome("A man a plan a canal Panama") == False
  assert is_palindrome("madam") == True
  assert is_palindrome("No lemon, no melon") == False
output: def is_palindrome(s):
      return s == s[::-1]