View Compilation Error

0_0_37779269_13420.cpp: In function 'void solve()':
0_0_37779269_13420.cpp:27:41: error: 'operator()' function uses 'auto' type specifier without trailing return type
         auto operator()(pair<int,int> x)const{
                                         ^
0_0_37779269_13420.cpp:27:41: note: deduced return type only available with -std=c++1y or -std=gnu++1y