设计推特

static int nowTweetTime = 0;
struct TweetContext {
    int t_time;
    int t_id;
};

class UserInformation {
public:
    std::vector<TweetContext> tList; // 推文列表
    std::set<int> followList;  // 关注列表

    void follow(int Id) {
        followList.insert(Id);
    }
    void unfollow(int Id) {
        followList.erase(Id);
    }
    void post(int Id) {
        TweetContext tweeter;
        tweeter.t_id = Id;
        tweeter.t_time = ++nowTweetTime;
        tList.emplace_back(tweeter);
        if (tList.size() > 10) {
            tList.erase(tList.begin());
        }
    }
};

class Twitter {
public:
    /** Initialize your data structure here. */
    Twitter() {
        
    }
    
    /** Compose a new tweet. */
    void postTweet(int userId, int tweetId) {
        userMap[userId].post(tweetId);
    }
    
    /** 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) {
        UserInformation user = userMap[userId];
        std::vector<TweetContext> newTweeterList;
        std::vector<int> feed;

        std::copy(user.tList.begin(), user.tList.end(), std::back_inserter(newTweeterList));  // 用户推文拷贝到新的推文中
        for(auto id : user.followList) { // 将关注列表的推文也放入新的推文中
            std::copy(userMap[id].tList.begin(), userMap[id].tList.end(), std::back_inserter(newTweeterList));
        }

        // 选出最近十条推文
        std::sort(newTweeterList.begin(), newTweeterList.end(), [](TweetContext& a, TweetContext& b){
                return a.t_time > b.t_time; 
        });
        int size = newTweeterList.size();
        if (size < 10) {
            for (int i = 0; i < size; ++i) {
                feed.emplace_back(newTweeterList[i].t_id);
            }
        }
        else {
            for (int i = 0; i < 10; ++i) {
                feed.emplace_back(newTweeterList[i].t_id);
            }
        }
        return feed;
    }
    
    /** Follower follows a followee. If the operation is invalid, it should be a no-op. */
    void follow(int followerId, int followeeId) {
        if (followerId != followeeId)
            userMap[followerId].follow(followeeId);
    }
    
    /** Follower unfollows a followee. If the operation is invalid, it should be a no-op. */
    void unfollow(int followerId, int followeeId) {
        if (userMap.find(followerId) == userMap.end()) return;
        userMap[followerId].unfollow(followeeId);
    }
private:
    std::map<int, UserInformation> userMap;
};

/**
 * 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);
 */

reference

leetcode