/in/foo.cc: In function 'int DFS(int, int)':
/in/foo.cc:28:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
for(int i=0;i<G[u].size();i++)
~^~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:75:9: warning: unused variable 'new_n' [-Wunused-variable]
int new_n=0;
^~~~~
/in/foo.cc:51:12: warning: iteration 499 invokes undefined behavior [-Waggressive-loop-optimizations]
pre2[i]=i;
~~~~~~~^~
/in/foo.cc:50:18: note: within this loop
for(int i=1;i<=maxn;i++)
~^~~~~~