125. Valid Palindrome

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

For example,
"A man, a plan, a canal: Panama"is a palindrome.
"race a car"isnota palindrome.

Note:
Have you consider that the string might be empty? This is a good question to ask during an interview.

For the purpose of this problem, we define empty string as valid palindrome.

Thought

Conver the string into lowercase and remove any non-word character (equal to [^a-zA-Z0-9_]) by regular expression.

→                   ←
amanaplanacanalpanama

Solution

public class Solution {
    public boolean isPalindrome(String s) {
        s = s.toLowerCase().replaceAll("\\W", "");
        for (int i = 0, j = s.length() - 1; i < j; i++, j--)
            if (s.charAt(i) != s.charAt(j)) return false;

        return true;   
    }
}