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

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

思路：

n個頂點和m條邊的圖，分別給出m條邊的兩端頂點，然後對其進行k次查詢，每次查詢輸入一個頂點集合，要求判斷這個頂點集合是否能完成頂點覆蓋，即圖中的每一條邊都至少有一個頂點在這個集合中。

C++：

#include "iostream"
#include "vector"
using namespace std;
vector<vector<int> > e;
int main(){
	int n,m,k;
	scanf("%d %d",&n,&m);
	e.resize(n);
	for (int i=0;i<m;i++)
	{
		int a,b;
		scanf("%d %d",&a,&b);
		e[a].push_back(i);
		e[b].push_back(i);
	}
	int N;
	scanf("%d",&k);
	for (int i=0;i<k;i++)
	{
		scanf("%d",&N);
		int flag=0,num;
		vector<int> hash(m, 0);
		for (int j=0;j<N;j++){
			scanf("%d",&num);
			for (int t = 0; t < e[num].size(); t++)
				hash[e[num][t]] = 1;
		}
		for (int j = 0; j < m; j++) {
			if (hash[j] == 0) {
				printf("No\n");
				flag = 1;
				break;
			}
		}
		if (flag == 0) printf("Yes\n");
	}
	return 0;
}