顶点覆盖问题。无向图G=(E，V)，寻找V的一个最小子集V’，使得图中所有边至少有一个顶点在集合V’中。输出V’包含的顶点数。-Vertex cover problem. To Figure G = (E, V), find V, a minimal subset of V ' , makes all the edges in the graph at least one vertex in the set V' . Output V ' contains the number of vertices.