125. Valid Palindrome (Array; Two-Pointers)

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) {
        if(s.empty()) return true;
        int sLength = s.length();
        int front = -1;
        int rear = sLength;
        char cFront;
        char cRear;
        while (1)
        {
                cFront = s[++front];
                cRear = s[--rear];
                if(front > rear) break;
                if(cFront <= 'Z'&& cFront >='A')
                {
                    cFront +=32;
                }
                if(cRear <= 'Z'&& cRear >='A')
                {
                    cRear +=32;
                }              
                while(  cFront < '0' || (cFront < 'a' && cFront > '9')|| cFront>'z')
                {
                    cFront = s[++front];
                    if(front >= rear) break;
                    if(cFront <= 'Z'&& cFront >='A')
                    {
                        cFront +=32;
                    }
                }
               while(  cRear < '0' || (cRear < 'a' && cRear > '9')|| cRear>'z')
                {
                    cRear = s[--rear];
                    if(front >= rear) break;
                    if(cRear <= 'Z'&& cRear >='A')
                   {
                       cRear +=32;
                    }
                }            
                if(front >= rear) break;
                if(cFront!=cRear)
                {
                    return false;
                }
            }
            return true;
    }
};