Valid Palindrome

Valid Palindrome

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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" is not a 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.

public class Solution {    public boolean isPalindrome(String s) {        if(s.isEmpty()) return true;        s = s.toLowerCase();        int start = 0, end = s.length()-1;        while(start < end){            char i = s.charAt(start), j = s.charAt(end);            if(!((i >='a' && i<='z') || (i>='0' && i<='9'))) {                start++;                continue;            }            if(!((j >='a' && j<='z') || (j>='0' && j<='9'))) {                end--;                continue;            }            if(s.charAt(start)!=s.charAt(end)) return false;            else {                start++;                end--;            }        }        return true;    }}