foo.cc: In function 'void dfs(int, int)':
foo.cc:19:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   19 |     for(int i = 0; i < tree[x].size(); i++) dfs(tree[x][i], color[x]);
      |                    ~~^~~~~~~~~~~~~~~~

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