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#include<map> #include<queue> class Solution { public: string FirstNonRepeating(string A){ map<char,int> visited; queue<char>q; string ans; for(auto i:A){ q.push(i); visited[i]++; while(!q.empty()){ if(visited[q.front()]>1){ q.pop(); }else{ ans.push_back(q.front()); break; } if(q.empty()) ans.push_back('#'); } } return ans; } };