leetcode 355. Design Twitter

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本文介绍了一个简化版Twitter的设计方案，包括发布推文、获取新闻动态、关注与取消关注等功能的具体实现方式。通过使用数据结构如map和set来高效地完成这些操作。

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355. Design Twitter

Design a simplified version of Twitter where users can post tweets, follow/unfollow another user and is able to see the 10 most recent tweets in the user's news feed. Your design should support the following methods:

postTweet(userId, tweetId): Compose a new tweet.
getNewsFeed(userId): 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.
follow(followerId, followeeId): Follower follows a followee.
unfollow(followerId, followeeId): Follower unfollows a followee.

Example:

Twitter twitter = new Twitter();

// User 1 posts a new tweet (id = 5).
twitter.postTweet(1, 5);

// User 1's news feed should return a list with 1 tweet id -> [5].
twitter.getNewsFeed(1);

// User 1 follows user 2.
twitter.follow(1, 2);

// User 2 posts a new tweet (id = 6).
twitter.postTweet(2, 6);

// User 1's news feed should return a list with 2 tweet ids -> [6, 5].
// Tweet id 6 should precede tweet id 5 because it is posted after tweet id 5.
twitter.getNewsFeed(1);

// User 1 unfollows user 2.
twitter.unfollow(1, 2);

// User 1's news feed should return a list with 1 tweet id -> [5],
// since user 1 is no longer following user 2.
twitter.getNewsFeed(1);

1、发表文章的先后使用map<int, pair<int,int>> key值存的是数字标记，标记时间先后。

2、unordered_map<int, set<int> >存的是关注的列表。

3、每一次遍历发表文章的map，判断这个文章的作者是不是当前查询的人或者他关注的人。如果是，就加入ret。

class Twitter {
public:
    /** Initialize your data structure here. */
    Twitter() 
    {
        this->onlynum = 0;
    }
    
    /** Compose a new tweet. */
    void postTweet(int userId, int tweetId) 
    {
        mp[onlynum] = make_pair(userId, tweetId);
        onlynum++;
    }
    
    /** 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. */
    vector<int> getNewsFeed(int userId) 
    {
        vector<int> ret;
        for (auto it = mp.rbegin(); it != mp.rend(); it ++)
        {
            int author = it->second.first;
            if (userId == author || user[userId].find(author) != user[userId].end())
                ret.push_back(it->second.second);
            
            if (ret.size() == 10)
                break;
        }
        return ret;
    }
    
    /** Follower follows a followee. If the operation is invalid, it should be a no-op. */
    void follow(int followerId, int followeeId) 
    {
        if (user.find(followerId) == user.end()) 
        {
            set<int> tmp;
            tmp.insert(followeeId);
            user[followerId] = tmp;
        }
        else
        {
            user[followerId].insert(followeeId);
        }
    }
    
    /** Follower unfollows a followee. If the operation is invalid, it should be a no-op. */
    void unfollow(int followerId, int followeeId) 
    {
        user[followerId].erase(followeeId); 
    }
private:
    map<int, pair<int, int>> mp;
    unordered_map<int, set<int> > user;
    int onlynum;
};

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