foo.cc: In function 'int dfs(int, int)':
foo.cc:19:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 0; i < G[cur].size(); ++i) {
                    ~~^~~~~~~~~~~~~~~
foo.cc: In function 'void dfs1(int)':
foo.cc:36:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 0; i < G[u].size(); ++i) {
                    ~~^~~~~~~~~~~~~
foo.cc: In function 'void Solve()':
foo.cc:57:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i = 0; i < G[u].size(); ++i) {
                        ~~^~~~~~~~~~~~~

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