View Compilation Error

0_0_33884327_540.cpp: In lambda function:
0_0_33884327_540.cpp:21:35: error: no match for call to '(std::function<void(unsigned int, unsigned int)>) (const unsigned int&)'
                     dfs1(it.second);
                                   ^
In file included from GCC4.9.2/x86_64-w64-mingw32/include/c++/x86_64-w64-mingw32/bits/stdc++.h:70:0,
                 from 0_0_33884327_540.cpp:1:
GCC4.9.2/x86_64-w64-mingw32/include/c++/functional:2142:11: note: candidate is:
     class function<_Res(_ArgTypes...)>
           ^
GCC4.9.2/x86_64-w64-mingw32/include/c++/functional:2434:5: note: _Res std::function<_Res(_ArgTypes ...)>::operator()(_ArgTypes ...) const [with _Res = void; _ArgTypes = {unsigned int, unsigned int}]
     function<_Res(_ArgTypes...)>::
     ^
GCC4.9.2/x86_64-w64-mingw32/include/c++/functional:2434:5: note:   candidate expects 2 arguments, 1 provided