C++ 代码

class Solution{
public:
    queue<char> q;
    unordered_map<char, int> hash;

    //Insert one char from stringstream
    void insert(char ch){
        if(++ hash[ch] == 1)
            q.push(ch);
    }
    //return the first appearence once char in current stringstream
    char firstAppearingOnce(){
        while(!q.empty() && hash[q.front()] > 1) q.pop();
        if(q.empty()) return '#';
        return q.front();
    }
};