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 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

#include <iostream>
#include <vector>
using namespace std;
int main() {
    int n, m, k, nv, a, b, num;
    scanf("%d%d", &n, &m);
    vector<int> v[n];
    for (int i = 0;i < m; i++) {
        scanf("%d%d", &a, &b);
        v[a].push_back(i);
        v[b].push_back(i);
    }
    scanf("%d", &k);
    for (int i = 0; i < k; i++) {
        scanf("%d", &nv);
        int flag = 0;
        vector<int> hash(m, 0);
        for (int j = 0; j < nv; j++) {
            scanf("%d", &num);
            for (int t = 0; t < v[num].size(); t++)
                hash[v[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;
}