剑指offer--46.字符流中第一个不重复的字符

class Solution {
    public:
        //Insert one char from stringstream
        void Insert(char ch) {
            ++mark[ch];
            if( mark[ch] == 1) {
                str.push_back(ch);
            }
        }
        //return the first appearence once char in current stringstream
        char FirstAppearingOnce() {
            while( !str.empty() && mark[str.front()] > 1) str.pop_front();
            if( str.empty() ) return ‘#‘;
            return str.front();
        }
    private:
        unsigned char mark[128];
        deque<char> str;
};