View Compilation Error

0_0_36693949_2397.cpp:21:1: error: 'vector' does not name a type
 vector<int> ans;
 ^
0_0_36693949_2397.cpp: In function 'bool dfs(int)':
0_0_36693949_2397.cpp:34:1: error: 'ans' was not declared in this scope
 ans.push_back(x);
 ^
0_0_36693949_2397.cpp: In function 'int main()':
0_0_36693949_2397.cpp:40:26: error: 'ans' was not declared in this scope
 memset(G, 0, sizeof(G)), ans.clear(), memset(vis, 0, sizeof(vis));
                          ^