[LeetCode] 355. 设计推特

不得不说 真的很强 根本想不到

package leetcode;

import java.util.*;

/**
 * @author doyinana
 * @create 2020-04-14 0:29
 */
public class Twitter {
    public static int timestamp=0;

    public class Tweet{
        public int tweetId;
        public int time;
        public Tweet next;
        public Tweet(int tweetId ,int time){
            this.tweetId = tweetId;
            this.time = time;
            this.next = null;
        }
    }

    public class User{
        private int userId;
        public Set<Integer> followed;
        public Tweet headTweet;

        public User(int userId){
            followed = new HashSet<>();
            this.userId = userId;
            this.headTweet = null;
            //用户关注一下自己
            follow(this.userId);
        }

        public void follow(int userId) {
            followed.add(userId);
        }

        public void unfollow(int userId) {
            // 不可以取关自己
            if (userId != this.userId)
                followed.remove(userId);
        }

        public void post(int tweetId){
            Tweet twt = new Tweet(tweetId,timestamp);
            timestamp++;
            twt.next=headTweet;
            headTweet=twt;
        }
    }

    private HashMap<Integer, User> userHashMap = new HashMap<>();

    public void postTweet(int userId,int tweetId){
        if(!userHashMap.containsKey(userId)){
            userHashMap.put(userId,new User(userId));
        }
        userHashMap.get(userId).post(tweetId);
    }

    public List<Integer> getNewsFeed(int userId){
        List<Integer> result=new ArrayList<>();
        if(!userHashMap.containsKey(userId)){
            return result;
        }
        Set<Integer> users=userHashMap.get(userId).followed;
        PriorityQueue<Tweet> priorityQueue=new PriorityQueue<>(users.size(),(a,b)->
                (b.time-a.time));
        for(int id:users){
            Tweet tweet=userHashMap.get(id).headTweet;
            if(tweet==null) continue;
            priorityQueue.add(tweet);
        }
        while(!priorityQueue.isEmpty()){
            if(result.size()==10){
                break;
            }
            Tweet tweet=priorityQueue.poll();
            result.add(tweet.tweetId);
            if(tweet.next!=null){
                priorityQueue.add(tweet.next);
            }
        }
        return result;
    }

    public void follow(int followerId,int followeeId){
        if(!userHashMap.containsKey(followerId)){
            userHashMap.put(followerId,new User(followerId));
        }
        if (!userHashMap.containsKey(followeeId)) {
            userHashMap.put(followeeId, new User(followeeId));
        }
        userHashMap.get(followerId).follow(followeeId);
    }

    public void unfollow(int followerId, int followeeId) {
        if (userHashMap.containsKey(followerId)) {
            userHashMap.get(followerId).unfollow(followeeId);
        }
    }
}