foo.cc: In function 'void bfs()':
foo.cc:31:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
              for(int i = 0; i < top.vec.size(); i++){
                             ~~^~~~~~~~~~~~~~~~
foo.cc:41:9: warning: this 'for' clause does not guard... [-Wmisleading-indentation]
         for(int i = 1; i <= n; i++)
         ^~~
foo.cc:46:13: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'for'
             if(!cnt)
             ^~

自豪地采用[jd5](https://github.com/masnn/jd5)进行评测