1 
                             #include<iostream>

                             2 
                             #include<algorithm>

                             3 
                             #include<vector>

                             4 
                             using 
                             namespace 
                             std; 
                             5 
                             6 
                             struct 
                             edge { 
                             7 
                             int 
                             st, ed; 
                             8 
                             }; 
                             9 
                             vector <
                             int 
                            > map[
                             100001 
                             ]; 
                             10 
                             vector <edge>
                             vec; 
                             11 
                             int 
                             main() { 
                             12 
                             13 
                             int 
                             n, m; 
                             14 
                                 cin >> n >>
                             m; 
                             15 
                             for 
                             (
                             int 
                             i = 
                             0 
                            ; i < m; i++
                             ) { 
                             16 
                             int 
                             st, ed; 
                             17 
                                     cin >> st >>
                             ed; 
                             18 
                                     vec.push_back({ st, ed }); 
                             // 
                             初始化存边的s数组 
                             19 
                             } 
                             20 
                             21 
                             for 
                             (
                             int 
                             i = 
                             0 
                            ; i < m; i++
                             ) 
                             22 
                             map[vec[i].st].push_back(i); 
                             23 
                             // 
                             初始化map数组，vec[i].st表示顶点，在该顶点加入其对应的边 
                             24 
                             25 
                             return 
                             0 
                             ; 
                             26 
                             }
                          
                        

                          
                             1 
                             void 
                             dfs(
                             int 
                             x) { 
                             2 
                                 cout << x<<
                             " 
                             " 
                             ; 
                             3 
                             4 
                             for 
                             (
                             int 
                             i = 
                             0 
                            ; i < map[x].size(); i++
                             ) 
                             5 
                             { 
                             6 
                             int 
                             j =
                             vec[map[x][i]].ed; 
                             7 
                             if 
                             (!
                             st[j]) 
                             8 
                             { 
                             9 
                                         st[j] = 
                             1 
                             ; 
                             10 
                             dfs(j); 
                             11 
                             } 
                             12 
                             } 
                             13 
                             }
                          
                        

                          
                             void 
                             add(
                             int 
                             a, 
                             int 
                             b) { e[idx] 
                            = b, ne[idx] = h[a], h[a] = idx++
                             ; }