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:
给出一些顶点,判断是否这些顶点的边能否包含全部的边。
stl中 set的使用。
代码如下:
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <vector>
#include <queue>
#include <map>
#include <set>
using namespace std;
const int maxn=1e4+5;
int n,m,k;
map<int,vector<int> >ma;
int a[1005];
int main()
{
scanf("%d%d",&n,&m);
for (int i=0;i<m;i++)
{
int x,y;
scanf("%d%d",&x,&y);
ma[x].push_back(i);
ma[y].push_back(i);
}
scanf("%d",&k);
while (k--)
{
int l;
scanf("%d",&l);
set<int>se;
for (int i=0;i<l;i++)
{
int x;
scanf("%d",&x);
for (int j=0;j<ma[x].size();j++)
{
se.insert(ma[x][j]);
}
}
if(se.size()==m)
{
printf("Yes\n");
}
else
{
printf("No\n");
}
}
return 0;
}