题目地址

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 <cstdio>
#include <cstring>
#include<iostream>
#include <vector>           //多好的办法，用每条边1到m代表每条边值；从而用vector可以存储邻接矩阵；
#include<math.h>
#include<string>
#include<queue>
#include <algorithm>
#include<set>
#include<map>
using namespace std;
const int  maxn= 5010,inf=1000000000;  //最大顶点数
int main(){
    int n,m,k,v1,v2;
    cin>>n>>m;vector<int> v[m+1];
    for(int i=0;i<m;i++){
        cin>>v1>>v2;
        v[v1].push_back(i);v[v2].push_back(i);          //most important ;store the idex of the edges;
    }
    cin>>k;
    for(int i=0;i<k;i++){
        int book[m+1]={0},query_cnt,v3;bool res=1;
        cin>>query_cnt;
        for(int j=0;j<query_cnt;j++){
            cin>>v3;
            for(int t=0;t<v[v3].size();t++) book[v[v3][t]]=1;           //let his edges be true；
        }
        for(int j=0;j<m;j++) if(!book[j]) {res=0;break;}            //m,not n;
        if(res) cout<<"Yes"<<endl;
        else cout<<"No"<<endl;
    }
}