/in/foo.cc: In function 'void DP(int)':
/in/foo.cc:14:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 0; i < son[k].size(); i++)
                         ~~^~~~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:32:13: warning: unused variable 'root' [-Wunused-variable]
         int root;
             ^~~~