description

A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers.

Given a string s, return true if it is a palindrome, or false otherwise.

 

Example 1:

Input: s = "A man, a plan, a canal: Panama"
Output: true
Explanation: "amanaplanacanalpanama" is a palindrome.

Example 2:

Input: s = "race a car"
Output: false
Explanation: "raceacar" is not a palindrome.

Example 3:

Input: s = " "
Output: true
Explanation: s is an empty string "" after removing non-alphanumeric characters.
Since an empty string reads the same forward and backward, it is a palindrome.

 

Constraints:

  • 1 <= s.length <= 2 * 105
  • s consists only of printable ASCII characters.

submission

// just use iterator
impl Solution {
    pub fn is_palindrome(s: String) -> bool {
        // don't collect them to avoid heap allocation
        let forward = s.chars()
            .filter(|ch| ch.is_alphanumeric())
            .map(|ch| ch.to_ascii_lowercase());
        let backward = s.chars()
            .rev()
            .filter(|ch| ch.is_alphanumeric())
            .map(|ch| ch.to_ascii_lowercase());
        forward.eq(backward)
    }
}