foo.cc: In function 'int Three(int, int*)':
foo.cc:14:6: warning: unused variable 'tmp' [-Wunused-variable]
  int tmp;
      ^~~
foo.cc:16:10: warning: 'i' may be used uninitialized in this function [-Wmaybe-uninitialized]
  for(int i;i<n;i++)
          ^
foo.cc:25:21: warning: 'j' may be used uninitialized in this function [-Wmaybe-uninitialized]
  if(res[2]!=0) Three(j,res);
                ~~~~~^~~~~~~

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。