foo.cc: In function 'int jiaohuancishu(std::vector<int>)':
foo.cc:23:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   23 |     for(int i=0;i<po.size();i++)
      |                 ~^~~~~~~~~~
foo.cc:26:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   26 |     for(int i=0;i<nums.size();i++)
      |                 ~^~~~~~~~~~~~

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