355. Design Twitter

            /** 355. Design Twitter * 2016-7-13 by Mingyang * System designs are really broken.*/        classTwitter {Private Static intTimestamp=0; //Easy to find if user exist            PrivateMap<integer, user>UserMap; //Tweet link to next tweet so, we can save a lot of time//When we execute Getnewsfeed (userId)            Private classtweet{ Public intID;  Public intTime ;  PublicTweet Next;  PublicTweets (intID) {                     This. ID =ID; time= timestamp++; Next=NULL; }            }                    //OO Design So User can follow, unfollow and post itself             Public classuser{ Public intID;  PublicSet<integer>followed;  PublicTweet Tweet_head;  PublicUser (intID) {                     This. id=ID; Followed=NewHashset<>(); Follow (ID); //First follow itselfTweet_head =NULL; }                 Public voidFollow (intID)                {Followed.add (ID); }                 Public voidUnfollow (intID)                {followed.remove (ID); }                //everytime user post a new tweet, add it to the head of the tweet list.                 Public voidPostintID) {Tweet T=NewTweet (ID); T.next=Tweet_head; Tweet_head=T; }            }            /**Initialize your data structure here.*/             PublicTwitter () {UserMap=NewHashmap<integer, user>(); }                        /**Compose a new tweet.*/             Public voidPosttweet (intUseridintTweetid) {                if(!Usermap.containskey (userId)) {User U=NewUser (userId);                Usermap.put (UserId, u);                                } usermap.get (UserId). Post (Tweetid); }            //Best part of this . //First get all tweets lists from one user including itself and all people it followed. //Second Add all heads to a max heap. Every time we poll a tweet with//largest time stamp from the heap and then we add their next tweet into the heap. //So after adding all heads we have need to add 9 tweets//Heap Before we get the most recent tweets.             PublicList<integer> Getnewsfeed (intuserId) {List<Integer> res =NewLinkedlist<>(); if(!usermap.containskey (USERID))returnRes; Set<Integer> users =Usermap.get (userId). followed; Priorityqueue<Tweet> q =NewPriorityqueue<tweet> (Users.size (),NewComparator<tweet>() {@Override Public intCompare (tweet i1, tweet i2) {returnI2.time-I1.time;                        }                }); //(A, B), (B.time-a.time));                 for(intuser:users) {Tweet T=usermap.get (user). Tweet_head; //very imporant! If we add null to the head we are screwed.                    if(t!=NULL) {Q.add (t); }                }                intN=0;  while(!q.isempty () && n<10) {Tweet T=Q.poll ();                  Res.add (t.id); N++; if(t.next!=NULL) Q.add (T.next); }                            returnRes; }                        /**Follower follows a followee. If The operation is invalid, it should be a no-op.*/             Public voidFollow (intFollowerid,intFolloweeid) {                if(!Usermap.containskey (Followerid)) {User U=NewUser (Followerid);                Usermap.put (Followerid, u); }                if(!Usermap.containskey (Followeeid)) {User U=NewUser (Followeeid);                Usermap.put (Followeeid, u);            } usermap.get (Followerid). Follow (Followeeid); }                        /**Follower unfollows a followee. If The operation is invalid, it should be a no-op.*/             Public voidUnfollow (intFollowerid,intFolloweeid) {                if(!usermap.containskey (followerid) | | followerid==Followeeid)return;            Usermap.get (Followerid). Unfollow (Followeeid); }        }

355. Design Twitter