C++中stringstream运用读入字符串句子中的单词

class Solution {
public:
    vector uncommonFromSentences(string s1, string s2) {
        unordered_map mp;
        vector ans;
        string s;
        stringstream a,b;
        a<>s)mp[s]++;
        while(b>>s)mp[s]++;

        for(auto m:mp){
            if(m.second==1){
                ans.push_back(m.first);
            }
        }
        return ans;
    }
};