字符流中第一个不重复的字符，很简单

string a;

public:
//Insert one char from stringstream
void Insert(char ch)
{
a.push_back(ch);

}

//return the first appearence once char in current stringstream
char FirstAppearingOnce()
{

        for(int i=0;i<a.length();i++){
           if(a.find_first_of(a[i])==a.find_last_of(a[i])) 
            return a[i];
        }
        return '#';


}

};