#include <string>
using std::string;
#include <cctype>

class Solution
{
public:
    bool isPalindrome(string s)
    {
        for (auto b = s.cbegin(), e = std::prev(s.cend()); b < e; ++b, --e)
        {
            while (!isalnum(*b))
                ++b;
            while (!isalnum(*e))
                --e;
            if (b < e && tolower(*b) != tolower(*e))
                return false;
        }
        return true;
    }
};