PAT (Advanced Level) Practice 1134 Vertex Cover (25分) （存边+标记点！！）

1.题目

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 N and M (both no more than 10​4​​), 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 K lines of queries follow, each in the format:

N​v​​ v[1] v[2]⋯v[N​v​​]

where N​v​​ 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

2.题目分析

将图中的所有边用struct记录，将待测试的点的大小用vector标记， 之后遍历图的边，如果边的两个点在vector中都未标记，则说明没有覆盖

3.代码

#include<iostream>
#include<vector>
using namespace std;
struct node
{ 
	int s, e;
};
vector<node>list;
int main()
{
	int n, m, a, b, k, count;
	scanf("%d %d", &n, &m);
	for (int i = 0; i < m; i++)
	{
		scanf("%d %d", &a, &b);
		list.push_back({ a,b });
	}
	scanf("%d", &k);
	for (int i = 0; i < k; i++)
	{
		bool ok = true;
		vector<int>mark;
		mark.resize(m);
		scanf("%d", &count);
		for (int j = 0; j < count; j++)
		{
			scanf("%d", &a);
			mark[a] = 1;
		}
		for (int s = 0; s < m; s++)
			if (mark[list[s].e] == 0 && mark[list[s].s] == 0) { ok = false; break; }
		if (ok)printf("Yes\n");
		else printf("No\n");
	}

}