It's a spanning tree if there's also at least one path between any two points, i.e., no network nodes are left unconnected.

如果任意两点之间有且只有一条通路，则构成了一棵生成树。即没有网络节点是孤立的。

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The minimum labeling spanning tree(MLST) problem is an NP-hard problem in which, given a graph with labeled edges, one seeks a spanning tree with the least number of labels.

最小标记生成树就是其中之一，它的目标是给出一个边上带有颜色的图，计算使用颜色种类最少的生成树。

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