pub fn is_palindrome(string: String) -> bool {
  let normalized = string.chars().filter_map(|c| {
    if char::is_alphanumeric(c) {
      Some(c.to_ascii_lowercase())
    } else {
      None
    }
  });

  let regular = normalized.clone().collect::<String>();
  let reversed = normalized.rev().collect::<String>();

  regular == reversed
}