foo.cc: In function 'bool spfa(int)':
foo.cc:23:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<Node>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   23 |         for (int i = 0; i < edge[u].size(); i++)
      |                         ~~^~~~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:51:13: warning: 's' is used uninitialized [-Wuninitialized]
   51 |     if (spfa(s))cout << -1;
      |         ~~~~^~~
foo.cc:42:9: note: 's' was declared here
   42 |     int s;
      |         ^

[Hydro](https://hydro.ac)提供评测服务