算法1

C++ 代码

class Solution{
    string s;
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++)
        {
            char a = s[i];
            if(s.find(a)==s.rfind(a))
            {
                return a;
            }
        }
        return '#';
    }
};