题解 | #病毒传播#

import java.util.ArrayList;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
import java.util.Scanner;

public class Main {
    private static HashSet<Integer> infected;
    private static HashSet<Integer>[] adj;
    private static int t;

    public static void main(String[] args){
        Scanner in = new Scanner(System.in);

        while(in.hasNext()){
            solution(in);
        }
    }

    /**
     * 模拟法: bfs
     * @param in
     */
    private static void solution(Scanner in){
        // 点数
        int V = in.nextInt();
        // 边数
        int E = in.nextInt();

        // 构建图 点的范围[1:V]
        adj = new HashSet[V+1];
        for(int i=1; i<=V; i++){
            adj[i] = new HashSet<>();
        }
        int v1,v2;
        for(int i=1; i<=E; i++){
            v1 = in.nextInt();
            v2 = in.nextInt();
            // 去环
            if(v1 != v2){
                adj[v1].add(v2);
                adj[v2].add(v1);
            }
        }

        // 感染病毒的点集infected
        int k = in.nextInt();
        t = in.nextInt();
        infected = new HashSet<>();
        for(int i=1; i<=k; i++){
            infected.add(in.nextInt());
        }

        // bfs
        List<Integer> result = new ArrayList<>();
        for(int i=1; i<=V; i++){
            if(bfs(i)){
                result.add(i);
            }
        }

        // 输出
        if(result.size() == 0){
            System.out.println(-1);
        }else{
            int size = result.size();
            for(int i=0; i<size-1; i++){
                System.out.print(result.get(i));
                System.out.print(" ");
            }
            System.out.print(result.get(size-1));
        }
    }

    /**
     * 广度优先搜索
     * @param start
     * @return
     */
    private static boolean bfs(int start){
        HashSet<Integer> visited = new HashSet<>();
        Queue<Integer> queue = new LinkedList<>();

        if(infected.contains(start)){
            visited.add(start);
            queue.offer(start);
        }

        int days = 0;
        while(!queue.isEmpty()){
            Integer u;
            for(int i=queue.size(); i > 0; i--){
                u = queue.poll();
                for(Integer v: adj[u]){
                    if(!infected.contains(v)){
                        return false;
                    }else if(!visited.contains(v)){
                        visited.add(v);
                        queue.offer(v);
                    }
                }
            }
            if(++days == t){
                break;
            }
        }
        
        return visited.size() == infected.size();
    }
}