【leetcode】355. Design Twitter

  1 public class Twitter {
  2     private static int order=0;
  3     private Map<Integer,Set<Message>> messages;
  4     private Map<Integer,Set<Integer>> followers;
  5     /** Initialize your data structure here. */
  6     public Twitter() {
  7         messages = new HashMap<Integer,Set<Message>>();
  8         followers = new HashMap<Integer,Set<Integer>>();
  9     }
 10    
 11     /** Compose a new tweet. */
 12     public void postTweet(int userId, int tweetId) {
 13         Message m = new Message(userId,tweetId,order++);
 14         Set<Message> set=messages.getOrDefault(userId, new HashSet<Message>());
 15         set.add(m);
 16         messages.put(userId, set);
 17     }
 18     
 19     /** 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. */
 20     public List<Integer> getNewsFeed(int userId) {
 21         List<Message> sets = new ArrayList<Message>();
 22         //userId发布的消息
 23         Set<Message> set = messages.getOrDefault(userId, new HashSet<Message>());
 24         sets.addAll(set);
 25         //找出他所关注的人发布的消息
 26         Set<Integer> follow = followers.get(userId);
 27         if(follow!=null){
 28             for(int i:follow){
 29                 set=messages.getOrDefault(i, new HashSet<Message>());
 30                 sets.addAll(set);
 31             }
 32         }
 33         //对找出的消息进行排序，并找出最近翻出的10条返回
 34         List<Integer> result=new ArrayList<Integer>();
 35         Compare c =new Compare();
 36         sets.sort(c);
 37         for(int i=0;i<sets.size()&&i<10;i++){
 38             Message m=sets.get(i);
 39             result.add(m.twitterId);
 40         }
 41         return result;
 42     }
 43     
 44     /** Follower follows a followee. If the operation is invalid, it should be a no-op. */
 45     public void follow(int followerId, int followeeId) {
 46         if(followeeId==followerId)
 47             return;
 48         Set<Integer> set = followers.getOrDefault(followerId, new HashSet<Integer>());
 49         set.add(followeeId);
 50         followers.put(followerId, set);
 51         
 52     }
 53     
 54     /** Follower unfollows a followee. If the operation is invalid, it should be a no-op. */
 55     public void unfollow(int followerId, int followeeId) {
 56         if(followeeId==followerId)
 57             return;
 58         if(!followers.containsKey(followerId)){
 59              ;
 60          }
 61          else{
 62              Set<Integer> set = followers.get(followerId);
 63              set.remove(followeeId);
 64              //如果userid的用户已经没有关注的人，讲他的记录从map中删除掉
 65              if(set.size()==0){
 66                  followers.remove(followerId);
 67              }
 68              else{
 69              followers.put(followerId, set);
 70              }
 71          }
 72     }
 73 }
 74 //封装一条twitter的类
 75 class Message{
 76     int userId;
 77     int twitterId;
 78     int order;
 79     public Message(int userId, int twitterId,int order) {
 80         super();
 81         this.userId = userId;
 82         this.twitterId = twitterId;
 83         this.order=order;
 84     }
 85 }
 86 //对消息进行排序的比较器
 87 class Compare implements Comparator<Message>{
 88 
 89     @Override
 90     public int compare(Message m1, Message m2) {
 91         // TODO Auto-generated method stub
 92         if(m1.order>m2.order)
 93             return -1;
 94         else if(m1.order<m2.order)
 95             return 1;
 96         else
 97             return 0;
 98     }
 99     
100 }