/in/foo.cc: In function 'void mergesort(int)':
/in/foo.cc:28:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j=0;j<v[i].size();j++)
                ~^~~~~~~~~~~~
/in/foo.cc:34:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j=0;j<v1[i].size();j++)
                ~^~~~~~~~~~~~~
/in/foo.cc:31:6: warning: unused variable 'k' [-Wunused-variable]
  int k,t=0;
      ^
/in/foo.cc:31:8: warning: unused variable 't' [-Wunused-variable]
  int k,t=0;
        ^