PAT 1134 题意

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1134 Vertex Cover（25 分）

A vertex cover of a graph is a set of vertices such that each edge of the graph is incident to at least one vertex of the set. Now given a graph with several vertex sets, you are supposed to tell if each of them is a vertex cover or not.

Input Specification:

Each input file contains one test case. For each case, the first line gives two positive integers Nand M (both no more than 104), being the total numbers of vertices and the edges, respectively. Then M lines follow, each describes an edge by giving the indices (from 0 to N−1) of the two ends of the edge.

After the graph, a positive integer K (≤ 100) is given, which is the number of queries. Then Klines of queries follow, each in the format:

Nv v[1] v[2]⋯v[Nv]

where Nv is the number of vertices in the set, and v[i]'s are the indices of the vertices.

Output Specification:

For each query, print in a line Yes if the set is a vertex cover, or No if not.

Sample Input:

10 11
8 7
6 8
4 5
8 4
8 1
1 2
1 4
9 8
9 1
1 0
2 4
5
4 0 3 8 4
6 6 1 7 5 4 9
3 1 8 4
2 2 8
7 9 8 7 6 5 4 2

Sample Output:

No
Yes
Yes
No
No

A vertex cover of a graph is a set of vertices such that each edge of the graph is incident to at least one vertex of the set.

翻译：如果一个集合内的所有顶点能够使得该图的任意边的其中一个顶点，则称为顶点覆盖。

分析：每个边都需要满足：边的至少一个顶点在集合内；

可认为：即集合内的顶点所关联的所有边与图内所有边相等，达到“覆盖”。

看题看了大半天也看不懂，也读不懂其他人的看了其他人AC的代码才看懂题。。。。。。