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
图论:给定一个图,再给定一个节点集合,判断这些节点能否包含所有的边。
hash思想:给每条edge标号。
#include <vector>
#include <iostream>
using namespace std;
bool visit[10010];
int main(){
int v,e,k;
scanf("%d %d",&v,&e);
std::vector<int> graph[10010];
for(int i=0;i<e;i++){
int a,b;
scanf("%d %d",&a,&b);
graph[a].push_back(i);
graph[b].push_back(i);
}
scanf("%d",&k);
for(int i=0;i<k;i++){
int tempnum,temp,num=0;
scanf("%d",&tempnum);
fill(visit,visit+10010,false);
for(int j=0;j<tempnum;j++){
scanf("%d",&temp);
for(int u=0;u<graph[temp].size();u++){
if(visit[graph[temp][u]]==false){
num++;
visit[graph[temp][u]]=true;
}
}
}
if(num==e)
printf("Yes\n");
else
printf("No\n");
}
}