View Compilation Error

0_0_18227380_26363.cpp: In function 'void bfs(int)':
0_0_18227380_26363.cpp:69:45: error: no match for 'operator[]' (operand types are 'std::set<int>' and 'int')
     for(int i = 0; i < sz; ++i) q.push(solve[i]);
                                             ^