/in/foo.cc: In function 'void dfs(int, int, int)':
/in/foo.cc:67:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 0; i < G[u].size(); i++)
                    ~~^~~~~~~~~~~~~
/in/foo.cc: In function 'L query(char)':
/in/foo.cc:132:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
/in/foo.cc:129:17: warning: 'flag' may be used uninitialized in this function [-Wmaybe-uninitialized]
      ans += flag*(lca(nxt, x) + lca(las, x) - lca(las, nxt));
             ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~