View Compilation Error

0_0_32178376_28227.cpp: In function 'void dfs(int, int)':
0_0_32178376_28227.cpp:44:42: error: invalid initialization of reference of type 'int&' from expression of type 'std::map<int, long long int>::mapped_type {aka long long int}'
             int &rem = mp[idx[v]][cur_dep];
                                          ^