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 1), 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 [ [
where Nv is the number of vertices in the set, and ['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
这道题考察读题,给定顶点,边,给定一个集合,查看每个边是否至少一个点在集合内。我们按题意进行判断即可。
#include <iostream> #include <unordered_set> using namespace std; int N, M, K, tmp, Nv; pair<int, int> p[99999]; int main() { cin >> N >> M; for(int i = 0; i < M; i++) cin >> p[i].first >> p[i].second; cin >> K; while(K--) { cin >> Nv; unordered_set<int> s; while(Nv--) { cin >> tmp; s.insert(tmp); } bool flag = true; for(int i = 0; i < M; i++) { if(s.find(p[i].first) == s.end() && s.find(p[i].second) == s.end()) { flag = false; break; } } printf("%s\n", flag ? "Yes" : "No"); } return 0; }