class Solution { public: //Insert one char from stringstream void Insert(char ch) { s += ch; } //return the first appearence once char in current stringstream char FirstAppearingOnce() { for(int i=0;i<s.length();i++){ if(count(s.begin(),s.end(),s[i]) == 1)return s[i]; } return '#'; } private: string s = ""; };