/in/foo.cc: In function 'void dfs(int)':
/in/foo.cc:20:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 0; i < g[u].size(); ++i) {
                    ~~^~~~~~~~~~~~~
/in/foo.cc: In function 'void dfs2(int)':
/in/foo.cc:33:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 0; i < g[u].size(); ++i) {
                    ~~^~~~~~~~~~~~~