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);

class Twitter {
private:struct P {int id, ref;P(int i = 0, int j = 0) :id(i), ref(j) {}inline bool operator<(const P &a) const { return ref > a.ref; }};
public:Twitter() { time = 1; }void postTweet(int userId, int tweetId) {userPost[userId].insert(P(tweetId, time++));userFollow[userId].insert(userId);}vector<int> getNewsFeed(int userId) {q.clear();vector<int> res;for(auto &r: userFollow[userId]) {int n = userPost[r].size();auto it = userPost[r].begin();n = min(n, 10);while(n--) {if(q.size() < 10) {q.insert(*it++);} else {auto c = q.end();if(*it < *--c) {q.erase(c);q.insert(*it++);}}}}for(auto &r: q) res.push_back(r.id);return res;}void follow(int followerId, int followeeId) {userFollow[followerId].insert(followeeId);}void unfollow(int followerId, int followeeId) {if(followerId == followeeId) return;userFollow[followerId].erase(followeeId);}
private:int time;set<P> q; unordered_map<int, set<P>> userPost;unordered_map<int, set<int>> userFollow;
};