foo.cc: In function 'void Bellman_Ford(long long int)':
foo.cc:28:22: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   28 |         for(ll k=0; k<q.size(); k++){//遍历所有点
      |                     ~^~~~~~~~~

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