剑指offer——字符流中第一个不重复的字符

#include <iostream>
#include <map>
#include <queue>
using namespace std;

class Solution
{
    private:
        map<char,int> Map;
        queue<char> letter;

    public:
        //Insert one char from stringstream
        void Insert(char ch){
            Map[ch]++;
            if(Map[ch] == 1){
                letter.push(ch);
            }
        }

        //return the first appearence once char in current stringstream
        char FirstAppearingOnce(){
            while(!letter.empty() && Map[letter.front()] >= 2){
                letter.pop();
            }
            if(letter.empty()){
                return '#'; 
            }else{
                return letter.front();
            }
        }
};