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 104), 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.
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
题意：问是否图中的每条边与询问的点有关联。
思路：记录每条边的两个点，判断是否该点被询问。
#include <bits/stdc++.h>
using namespace std;
const int maxn=1e4+5;
int vis[maxn]={0};
int vv[maxn]={0};
vector<int >v[maxn];
struct node{
int a,b;
}lin[maxn];
int main()
{
int n,m;
scanf("%d%d",&n,&m);
int a,b;
for(int i=0;i<m;i++)
{
scanf("%d%d",&a,&b);
lin[i].a=a;
lin[i].b=b;
}
int q;scanf("%d",&q);
while(q--)
{
int k;
memset(vv,0,sizeof(vv));
scanf("%d",&k);
int flag=1;
//set <int>ask;
for(int i=0;i<k;i++)
{
scanf("%d",&a);
vv[a]=1;
}
for(int i=0;i<m;i++)
{
a=lin[i].a;
b=lin[i].b;
if(vv[a]||vv[b])continue;
else {
flag=0;break;
}
}
if(flag)printf("Yes\n");
else printf("No\n");
}
}
