input: Write a function to check if a given string is a palindrome. A palindrome is a string that reads the same backward as forward. If the given string is a palindrome, return True; otherwise, return False.
  def is_palindrome(s):
    s = s.lower().replace(" ", "")
    return s == s[::-1]
  
  assert is_palindrome("racecar") == True
  assert is_palindrome("A man a plan a canal Panama") == True
  assert is_palindrome("hello") == False
  assert is_palindrome("") == True
  assert is_palindrome("12321") == True
output: def is_palindrome(s):
    s = s.lower().replace(" ", "")
    return s == s[::-1]