/in/foo.cc: In function 'void dp(int)':
/in/foo.cc:12:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<son[x].size();i++)
              ~^~~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:31:8: warning: unused variable 'y' [-Wunused-variable]
  int x,y;
        ^