[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.

明天就是五一小长假了，突然有点失落呀，每次放假都有点囧~~ 这是一个非常非常无聊的题，符合现在的心情，所以就写写了。。。

class Solution {
public:
    bool isPalindrome(string s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int p=0, q=s.size()-1;
        
        while(p<q){            
            if(!((s[p] >= 'a' && s[p] <= 'z') || (s[p] >= 'A' && s[p] <= 'Z') ||(s[p] - '0' >= 0 && s[p] -'0'<=9))) {
                p++;
                continue;
            }
            if(!((s[q] >= 'a' && s[q] <= 'z') || (s[q] >= 'A' && s[q] <= 'Z') ||(s[q] - '0' >= 0 && s[q] -'0'<=9))) {
                q--;
                continue;
            }
            
            if(s[p]!=s[q] && s[p]-s[q] != 'A'-'a' && s[p]-s[q] != 'a'-'A') 
                return false;
            p++;
            q--;           
        }
        return true;
        
    }
};