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题意定义一张图的密度为它的边数与点数的比值。给定一张\(n\)个点、\(m=dn\)条边的无向图，记点集为\(V\)。你需要判断，任取\(V\)的非空真子集\(X\)，\(X\)的导出子图的密度是否一定严格小于\(d\)。多测，\(1\leqn,d,\summ\leq50000\)。题解对于一张流网络，记\(s,