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 <algorithm>
#include <cmath>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <string>
#include <cctype>
#include <string.h>
#include <cstdio>
#include <unordered_set>
using namespace std;
int main() {
int n,m,a,b,k,nv,num;
cin>>n>>m;
vector<int> v[n];
for(int i=0;i<m;i++){
cin>>a>>b;
v[a].push_back(i);
v[b].push_back(i);
}
cin>>k;
for(int i=0;i<k;i++){
cin>>nv;
int flag=0;
vector<int> hash(m,0);
for(int j=0;j<nv;j++){
cin>>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){
cout<<"No\n";
flag=1;
break;
}
}
if(flag==0) cout<<"Yes\n";
}
return 0;
}