foo.cc: In function 'int findmax(std::vector<int>&, int)':
foo.cc:11:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=1,j=w+1;j<a.size();i++,j++,k++)
                    ~^~~~~~~~~
foo.cc:14:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=1;i<tmp.size();i++)
              ~^~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务