leetcode-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" 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.

class Solution {public:    bool isPalindrome(string s) {        int n = s.length();        if(n == 0)return true;        int i = 0;        int j = n-1;        while(i < j)        {            while(!((s[i]>='a'&&s[i]<='z')||(s[i]>='A'&&s[i]<='Z')||(s[i]>='0'&&s[i] <='9')))            {                i++;                if(i == n-1)return true;            }            while(!((s[j]>='a'&&s[j]<='z')||(s[j]>='A'&&s[j]<='Z')||(s[j]>='0'&&s[j] <='9')))j--;                        if((s[i] != s[j])&&(s[i] != s[j]+32)&&(s[i] != s[j]-32))return false;            i++;            j--;        }                return true;    }};