一、题目
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二、题目大意
每条边至少有一个顶点出现在集合中。
三、考点
SET
四、注意
1、读懂题目。
五、代码
#include<iostream>
#include<vector>
#include<set>
#define N 10001
using namespace std;
bool e[N][N] = { false };
int main() {
//read
int n, m;
cin >> n >> m;
vector<vector<int>> v(m);
for (int i = 0; i < m; ++i) {
int a, b;
cin >> a >> b;
v[i].push_back(a);
v[i].push_back(b);
}
//query
int l;
cin >> l;
while(l--) {
//read
int k;
cin >> k;
set<int> sset;
for (int i = 0; i < k; ++i) {
int a;
cin >> a;
sset.insert(a);
}
//judge
bool flag = true;
for (int i = 0; i < m; ++i) {
//not find
if (sset.find(v[i][0]) == sset.end() && sset.find(v[i][1]) == sset.end()) {
flag = false;
break;
}
}
//output
if (flag == true)
cout << "Yes" << endl;
else
cout << "No" << endl;
}
system("pause");
return 0;
}