Leetcode 355. 设计推特-优快云博客

本文链接：https://blog.youkuaiyun.com/Aetherzzz/article/details/115316612

本文介绍了如何构建一个Twitter类，包含用户关注、推文发布、新闻推送和社交关系管理等功能，展示了核心数据结构和关键操作的实现细节。

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355. 设计推特

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class Twitter {
	// <用户ID, 该用户关注的人>
    private HashMap<Integer, Set<Integer>> followUsers;
    // <用户ID， <推文ID, 推文发布时间>>
    private HashMap<Integer, HashMap<Integer, Integer>> tweets;
    // 用于记录推文发布的时间
    private int time;

    /** Initialize your data structure here. */
    public Twitter() {
        this.time = 0;
        followUsers = new HashMap<>();
        tweets = new HashMap<>();
    }
    
    /** Compose a new tweet. */
    public void postTweet(int userId, int tweetId) {
        if(tweets.containsKey(userId)){
            tweets.get(userId).put(tweetId, time++);
        }else{
            HashMap<Integer, Integer> temp = new HashMap<>();
            temp.put(tweetId, time++);
            tweets.put(userId, temp);
        }
    }
    
    /** Retrieve the 10 most recent tweet ids in the user's news feed. Each item in the news feed must be posted by users who the user followed or by the user herself. Tweets must be ordered from most recent to least recent. */
    public List<Integer> getNewsFeed(int userId) {
        HashMap<Integer, Integer> map = new HashMap<>();
        if(followUsers.containsKey(userId)){
            for(Integer s : followUsers.get(userId)){
                if(tweets.containsKey(s)){
                    for(Map.Entry<Integer, Integer> entry : tweets.get(s).entrySet()){
                        map.put(entry.getKey(), entry.getValue());
                    }
                }
            }
        }
        if(tweets.containsKey(userId)){
            for(Map.Entry<Integer, Integer> entry : tweets.get(userId).entrySet()){
                map.put(entry.getKey(), entry.getValue());
            }
        }
        List<Map.Entry<Integer, Integer>> list = new ArrayList<>(map.entrySet());
        Collections.sort(list, (o1, o2) -> {
            return o2.getValue() - o1.getValue();
        });
        List<Integer> res = new ArrayList<>();
        int index = 0;
        for(Map.Entry<Integer, Integer> entry : list){
            res.add(entry.getKey());
            index++;
            if(index == 10) return res;
        }
        return res;
    }
    
    /** Follower follows a followee. If the operation is invalid, it should be a no-op. */
    public void follow(int followerId, int followeeId) {
        if(followerId == followeeId) return;
        if(followUsers.containsKey(followerId)){
            followUsers.get(followerId).add(followeeId);
        }else{
            Set<Integer> temp = new HashSet<>();
            temp.add(followeeId);
            followUsers.put(followerId, temp);
        }
    }
    
    /** Follower unfollows a followee. If the operation is invalid, it should be a no-op. */
    public void unfollow(int followerId, int followeeId) {
        if(followerId == followeeId) return;
        if(followUsers.containsKey(followerId)){
            followUsers.get(followerId).remove(followeeId);
        }else{
            return;
        }
    }
}

/**
 * Your Twitter object will be instantiated and called as such:
 * Twitter obj = new Twitter();
 * obj.postTweet(userId,tweetId);
 * List<Integer> param_2 = obj.getNewsFeed(userId);
 * obj.follow(followerId,followeeId);
 * obj.unfollow(followerId,followeeId);
 */