isPalindrome

// http://leetcode.com/onlinejudge#question_125

class Solution {
public:
    bool isPalindrome(string s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(s.empty()) {return true;}

        const size_t N = s.size();
        size_t i = 0, j = N - 1;
        for(;i<j;)
        {
            const char a = s[i];
            if(!isalnum(a)) { ++i; continue; }

            const char b = s[j];
            if(!isalnum(b)) { --j; continue; }

            if(tolower(a) != tolower(b)) { return false;}
            ++i; --j;
        }
        return true;
    }
};