Valid Palindrome

class Solution {public:    bool isPalindrome(string s) {        // Note: The Solution object is instantiated only once and is reused by each test case.        int i=0, j=s.size()-1;        while (i<j) {            while (i<j && (!((s[i]>='a' && s[i]<='z') || (s[i]>='A' && s[i]<='Z') || (s[i]>='0' && s[i]<='9')))) {                i++;            }            if (i>=j) 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]-'A'+'a' || s[i]-'A'+'a'==s[j])) {                return false;            }            i++;            j--;        }        return true;    }};