125. Valid Palindrome

class Solution { public: bool isPalindrome(string s) { if (s == "") return true; std::deque<char> dq; for (const char & c : s){ if (!std::isalpha(c) && !std::isdigit(c)) continue; else { if (std::isalpha(c)) dq.push_back(std::tolower(c)); else dq.push_back(c); } } while(!dq.empty()){ if (dq.front() != dq.back()) return false; else{ if (dq.size() == 1) return true; else{ dq.pop_front(); dq.pop_back(); } } } return true; } };