public class Solution
extends Object
125 - Valid Palindrome\.
Easy
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.