Leetcode-355 Design Twitter(设计推特)

struct cmp
{
    bool operator()(const pair<int,int> p1, const pair<int,int> p2)
    {
        return p1.first > p2.first; //first的小值优先
    }
};

class Twitter
{
    private:
        map<int,pair<set<int>,vector<pair<int,int>>>> PersonList;
        int time;
    public:
        /** Initialize your data structure here. */
        Twitter()
        {
            time = 0;
        }

        /** Compose a new tweet. */
        void postTweet(int userId, int tweetId)
        {
            auto ptr_to_user = PersonList.find(userId);
            if(ptr_to_user==PersonList.end())
            {
                set<int> FollowList;
                vector<pair<int,int>> PostList;
                PostList.push_back(make_pair(time,tweetId));
                FollowList.insert(userId);
                PersonList.insert(make_pair(userId,make_pair(FollowList,PostList)));
            }
            else
            {
                ptr_to_user -> second.second.push_back(make_pair(time,tweetId));
            }
            time ++;
        }

        /** 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> result;
            auto ptr_to_user = PersonList.find(userId);
            if(ptr_to_user==PersonList.end())
                return result;
            auto ptr_to_followlist = ptr_to_user->second.first.begin();

            priority_queue<pair<int,int>, vector<pair<int,int>>, cmp> Q;
            for(auto followeeid:ptr_to_user->second.first)
            {
                auto ptr_to_followee = PersonList.find(followeeid);
                for(auto p:ptr_to_followee->second.second)
                {
                    if(Q.size()<10)
                    {
                        Q.push(make_pair(p.first,p.second));
                    }
                    else
                    {
                        if(p.first>Q.top().first)
                        {
                            Q.pop();
                            Q.push(make_pair(p.first,p.second));
                        }
                    }
                }
            }

            while(!Q.empty())
            {
                result.emplace_back(Q.top().second);
                Q.pop();
            }
            reverse(result.begin(),result.end());
            return result;
        }

        /** Follower follows a followee. If the operation is invalid, it should be a no-op. */
        void follow(int followerId, int followeeId)
        {
            auto ptr_to_follower = PersonList.find(followerId);
            auto ptr_to_followee = PersonList.find(followeeId);
            if(ptr_to_follower==PersonList.end() && ptr_to_followee!=PersonList.end())
            {
                set<int> FollowList;
                vector<pair<int,int>> PostList;
                FollowList.insert(followeeId);
                FollowList.insert(followerId);
                PersonList.insert(make_pair(followerId,make_pair(FollowList,PostList)));
            }
            else if(ptr_to_follower!=PersonList.end()&&ptr_to_followee==PersonList.end())
            {
                set<int> FollowList;
                vector<pair<int,int>> PostList;
                FollowList.insert(followeeId);
                PersonList.insert(make_pair(followeeId,make_pair(FollowList,PostList)));
                ptr_to_follower -> second.first.insert(followeeId);
            }
            else if(ptr_to_follower==PersonList.end()&&ptr_to_followee==PersonList.end())
            {
                set<int> FollowList;
                vector<pair<int,int>> PostList;
                FollowList.insert(followeeId);
                PersonList.insert(make_pair(followeeId,make_pair(FollowList,PostList)));
                set<int> FollowList_;
                vector<pair<int,int>> PostList_;
                FollowList_.insert(followeeId);
                FollowList_.insert(followerId);
                PersonList.insert(make_pair(followerId,make_pair(FollowList_,PostList_)));
            }
            else
            {
                ptr_to_follower -> second.first.insert(followeeId);
            }
        }

        /** Follower unfollows a followee. If the operation is invalid, it should be a no-op. */
        void unfollow(int followerId, int followeeId)
        {
            if(followerId==followeeId)
                return ;
            auto ptr_to_follower = PersonList.find(followerId);
            if(ptr_to_follower==PersonList.end())
            {
                set<int> FollowList;
                vector<pair<int,int>> PostList;
                FollowList.insert(followerId);
                PersonList.insert(make_pair(followerId,make_pair(FollowList,PostList)));
                return ;
            }
            ptr_to_follower -> second.first.erase(followeeId);
        }
};

 其实可以把初始化创建人的ID的过程给抽出来做成一个函数，不过这只博主就是懒辣~