/in/foo.cc: In function 'int main()':
/in/foo.cc:35:30: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<Edge>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   35 |                 for(int i=0;i<g[P].size();i++)// 路线1：P -> Q
      |                             ~^~~~~~~~~~~~
/in/foo.cc:40:38: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<Edge>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   40 |                         for(int j=0;j<g[Q].size();j++)//路线2：Q -> R
      |                                     ~^~~~~~~~~~~~
/in/foo.cc:45:46: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<Edge>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   45 |                                 for(int k=0;k<g[R].size();k++)//路线3：R -> S
      |                                             ~^~~~~~~~~~~~
/in/foo.cc:50:54: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<Edge>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   50 |                                         for(int t=0;t<g[S].size();t++)//路线4：S->P必须回到P
      |                                                     ~^~~~~~~~~~~~