VertexCount[g] 给出对图 g 中顶点数的计数.
VertexCount[g, patt]给定匹配模式 patt 的顶点数的计数.
计算顶点数：
对匹配某个模式的顶点计数：
VertexList EdgeCount AdjacencyMatrix IncidenceMatrix Graph
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