View Compilation Error

0_0_31674001_13648.cpp: In function 'int dfs(int, int, int)':
0_0_31674001_13648.cpp:36:16: error: invalid initialization of non-const reference of type 'int&' from an rvalue of type 'int'
     for(int &i=0;i<mp[u].size();i++){
                ^