combinatorics heuristics greedy-algorithms steiner-tree connected-dominating-set distributed-algorithms graph-convolutional-networks steiner-tree-problem combinatorial-optimization approximation-algorithms distributed-algorithm deterministic-policy-gradients twin-networks graph-neural-networks minimum-weighted-dominating-set graph-convolutional-neural-networks maximum-weighted-independent-set node-weighted-steiner-tree moser-tardos-algorithm twin-based-critic