PAT 甲级 1134 Vertex Cover

https://pintia.cn/problem-sets/994805342720868352/problems/994805346428633088

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:

N​v​​ [ [

where N​v​​ 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

代码：

#include <bits/stdc++.h>
using namespace std;

const int maxn = 1e5 + 10;

int N, M, T, K;
int x, vis[maxn];

vector<int> v[maxn];
bool flag = false;
int step = 0;

int main() {
    scanf("%d%d", &N, &M);
    for(int i = 0; i < M; i ++) {
        int st, en;
        scanf("%d%d", &st, &en);

        v[st].push_back(i);
        v[en].push_back(i);
    }
    scanf("%d", &T);
    while(T --) {
        step = 0;
        memset(vis, 0, sizeof(vis));
        scanf("%d", &K);
        for(int i = 0; i < K; i ++){
            scanf("%d", &x);

            for(int j = 0; j < v[x].size(); j ++) {
                if(vis[v[x][j]] == 0) {
                    vis[v[x][j]] = 1;
                    step ++;
                }
            }

        }

        if(step == M) printf("Yes\n");
        else printf("No\n");
    }
    return 0;
}

　　标记边被覆盖的数量 判断数目是否符合 行吧 理解错题意可还行