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:

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.

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

No
Yes
Yes
No
No

解答

#include<iostream>
#include<vector>
#include<unordered_map>

using namespace std;

int main()
{
int vNum, eNum, u, v;
cin >> vNum >> eNum;
vector<vector<int>> mp(vNum);
for (int i = 0; i < eNum; i++) {
cin >> u >> v;
mp[u].push_back(i);
mp[v].push_back(i);
}
int qNum;
cin >> qNum;
for (int i = 0; i < qNum; i++) {
int n;
cin >> n;
unordered_map<int, bool> tmp;
for (int j = 0; j < n; j++) {
cin >> u;
for (auto it = mp[u].begin(); it != mp[u].end(); it++)
tmp[*it] = true;
}
if (tmp.size() == eNum) printf("Yes\n");
else printf("No\n");
}
return 0;
}