leetcode-355 设计推特

题目描述：设计一个简化版的推特(Twitter)，可以让用户实现发送推文，关注/取消关注其他用户，能够看见关注人（包括自己）的最近十条推文。你的设计需要支持以下的几个功能：

1. postTweet(userId, tweetId): 创建一条新的推文
2. getNewsFeed(userId): 检索最近的十条推文。每个推文都必须是由此用户关注的人或者是用户自己发出的。推文必须按照时间顺序由最近的开始排序。
3. follow(followerId, followeeId): 关注一个用户
4. unfollow(followerId, followeeId): 取消关注一个用户

代码实现

class Tweet implements Comparable<Tweet> {
    private Integer tweetId;

    private Long createTime;

    public Tweet(Integer tweetId, Long createTime) {
        this.tweetId = tweetId;
        this.createTime = createTime;
    }

    public Integer getTweetId() {
        return tweetId;
    }

    public void setTweetId(Integer tweetId) {
        this.tweetId = tweetId;
    }

    public Long getCreateTime() {
        return createTime;
    }

    public void setCreateTime(Long createTime) {
        this.createTime = createTime;
    }

    @Override
    public int compareTo(Tweet o) {
        return (int) (this.createTime - o.getCreateTime());
    }

    @Override
    public String toString() {
        return "Tweet{" +
                "tweetId=" + tweetId +
                ", createTime=" + createTime +
                '}';
    }
}

class User {
    private Integer userId;

    private List<Integer> followerIds;

    private List<Integer> followeeIds;

    private LinkedList<Tweet> tweets;

    public User(Integer userId, List<Integer> followerIds, List<Integer> followeeIds, LinkedList<Tweet> tweets) {
        this.userId = userId;
        this.followerIds = followerIds;
        this.followeeIds = followeeIds;
        this.tweets = tweets;
    }

    public Integer getUserId() {
        return userId;
    }

    public void setUserId(Integer userId) {
        this.userId = userId;
    }

    public List<Integer> getFollowerIds() {
        return followerIds;
    }

    public void setFollowerIds(List<Integer> followerIds) {
        this.followerIds = followerIds;
    }

    public List<Integer> getFolloweeIds() {
        return followeeIds;
    }

    public void setFolloweeIds(List<Integer> followeeIds) {
        this.followeeIds = followeeIds;
    }

    public LinkedList<Tweet> getTweets() {
        return tweets;
    }

    public void setTweets(LinkedList<Tweet> tweets) {
        this.tweets = tweets;
    }

    @Override
    public String toString() {
        return "User{" +
                "userId=" + userId +
                ", followerIds=" + followerIds +
                ", followeeIds=" + followeeIds +
                ", tweets=" + tweets +
                '}';
    }
}

class Twitter {
    private Map<Integer, User> users;

    public Twitter() {
        this.users = new HashMap<>();
    }

    public void postTweet(int userId, int tweetId) {
        Tweet tweet = new Tweet(tweetId, System.nanoTime());
        User user = this.users.getOrDefault(userId, createUser(userId));
        user.getTweets().addFirst(tweet);
        if (user.getTweets().size() > 10) {
            user.getTweets().subList(0, 10);
        }
        this.users.put(userId, user);
    }

    public List<Integer> getNewsFeed(int userId) {
        if (this.users.containsKey(userId)) {
            List<Tweet> tweets = new LinkedList<>();
            tweets.addAll(this.users.get(userId).getTweets());
            this.users.get(userId).getFollowerIds().stream().map(this.users::get).map(User::getTweets).forEach(list -> tweets.addAll(list));
            List<Integer> result = tweets.stream().sorted(Comparator.reverseOrder()).distinct().map(Tweet::getTweetId).collect(Collectors.toList());
            return result.size() > 10 ? result.subList(0, 10) : result;
        }
        return new ArrayList<>();
    }

    public void follow(int followerId, int followeeId) {
        User follower = this.users.getOrDefault(followerId, createUser(followerId));
        follower.getFollowerIds().add(followeeId);
        this.users.put(followerId, follower);
        User followee = this.users.getOrDefault(followeeId, createUser(followeeId));
        followee.getFolloweeIds().add(followerId);
        this.users.put(followeeId, followee);
    }

    public void unfollow(int followerId, int followeeId) {
        this.users.get(followerId).getFollowerIds().remove((Object) followeeId);
        this.users.get(followeeId).getFolloweeIds().remove((Object) followerId);
    }

    private User createUser(Integer userId) {
        return new User(userId, new ArrayList<>(), new ArrayList<>(), new LinkedList<>());
    }
}