1134. Vertex Cover (25)

时间限制

600 ms

内存限制

65536 kB

代码长度限制

16000 B

判题程序

Standard

作者

CHEN, Yue

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:

10 118 76 84 58 48 11 21 49 89 11 02 454 0 3 8 46 6 1 7 5 4 93 1 8 42 2 87 9 8 7 6 5 4 2

Sample Output:

NoYesYesNoNo

实力不够

实力不够

实力不够

一开始用邻接矩阵写，结果内存超了。。。

后来用set做，erase 相当于删边 ，结束的时候若还有边，则size不为零，不满足要求。考试的时候过了，怎么现在最后2点超时了。。。

#include<stdio.h>#include<vector>#include<set>using namespace std;set<int>adj[10010];set<int>tempadj[10010];vector<int>dele;void init(int n){int i;for(i=0;i<n;i++){tempadj[i]=adj[i];}}int main(){int n,m,k,i,j,c1,c2,num,z;scanf("%d %d",&n,&m);for(i=0;i<m;i++){scanf("%d %d",&c1,&c2);adj[c1].insert(c2);adj[c2].insert(c1);}scanf("%d",&k);for(i=0;i<k;i++){scanf("%d",&num);init(n);dele.clear();for(j=0;j<num;j++){scanf("%d",&c1);set<int>::iterator it=tempadj[c1].begin();for(;it!=tempadj[c1].end();it++){int next=*it;tempadj[next].erase(c1);dele.push_back(next);}for(z=0;z<dele.size();z++){tempadj[c1].erase(dele[z]);}}int flag=1;for(j=0;j<n;j++){if(tempadj[j].size()!=0){flag=0;break;}}if(flag){printf("Yes\n");}else{printf("No\n");}}}

参看了别人的博客：

#include<stdio.h>#include<vector>using namespace std;vector<int>adj[10010];vector<int>temp;int visit[10010];void init(int n){int i;for(i=0;i<n;i++){visit[i]=0;}}int main(){int n,m,i,j,c1,c2,k,num,z;scanf("%d %d",&n,&m);for(i=0;i<m;i++){scanf("%d %d",&c1,&c2);adj[c1].push_back(c2);adj[c2].push_back(c1);}scanf("%d",&k);for(i=0;i<k;i++){scanf("%d",&num);temp.clear();init(n);for(j=0;j<num;j++){scanf("%d",&c1);temp.push_back(c1);}int cou=0;for(j=0;j<temp.size();j++){for(z=0;z<adj[temp[j]].size();z++){int next=adj[temp[j]][z];if(visit[next]==0){cou++;}}visit[temp[j]]=1;}if(cou==m){printf("Yes\n");}else{printf("No\n");}}}