foo.cc: In function 'void mergesort(int)':
foo.cc:27:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j=0;j<v[i].size();j++)
                ~^~~~~~~~~~~~
foo.cc:33:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j=0;j<v1[i].size();j++)
                ~^~~~~~~~~~~~~
foo.cc:30:6: warning: unused variable 'k' [-Wunused-variable]
  int k,t=0;
      ^
foo.cc:30:8: warning: unused variable 't' [-Wunused-variable]
  int k,t=0;
        ^

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