算法1

懒人做法，迟更新

记录下已经重复的数字

C++ 代码

class Solution{
public:
    //Insert one char from stringstream

    queue<char> que;
    unordered_map<char,int> mp;
    void insert(char ch){
        if (mp[ch] == 0) {
            que.push(ch);
        }
        mp[ch] += 1;
    }
    //return the first appearence once char in current stringstream
    char firstAppearingOnce(){
        while (!que.empty() && mp[que.front()] >= 2) {
            que.pop();
        }
        return que.empty() ? '#' : que.front();
    }
};