leetcode-java/src/DesignTwitter355.java at master · fluency03/leetcode-java · GitHub

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/**
 * Design a simplified version of Twitter where users can post tweets,
 * follow/unfollow another user and is able to see the 10 most recent tweets
 * in the user's news feed. Your design should support the following methods:
 *
 * postTweet(userId, tweetId): Compose a new tweet.
 *
 * getNewsFeed(userId): 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.
 *
 * follow(followerId, followeeId): Follower follows a followee.
 *
 * unfollow(followerId, followeeId): Follower unfollows a followee.
 *
 * Example:
 *
 * 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);
 */


publicclassDesignTwitter355 {
classTwitter {
privateinttime = 0;
privateMap<Integer, User> map = newHashMap<>();
privatestaticfinalComparator<Tweet> comp = (t1, t2) -> Long.compare(t2.timestamp, t1.timestamp);

/** Initialize your data structure here. */
publicTwitter() {
 }

/** Compose a new tweet. */
publicvoidpostTweet(intuserId, inttweetId) {
if (!map.containsKey(userId)) map.put(userId, newUser(userId));
map.get(userId).addTweet(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.
 */
publicList<Integer> getNewsFeed(intuserId) {
PriorityQueue<Tweet> pq = newPriorityQueue<>(10, comp);
if (!map.containsKey(userId)) returnnewArrayList<Integer>();
Userme = map.get(userId);
for (Integeruid: me.following) {
pq.addAll(map.get(uid).tweets);
 }
pq.addAll(me.tweets);
List<Integer> ids = newArrayList<>();
intsize = pq.size();
for (inti=0; i<10 && i<size; i++) {
ids.add(pq.poll().id);
 }
returnids;
 }

/**
 * Follower follows a followee. If the operation is invalid,
 * it should be a no-op.
 */
publicvoidfollow(intfollowerId, intfolloweeId) {
if (!map.containsKey(followerId)) map.put(followerId, newUser(followerId));
if (!map.containsKey(followeeId)) map.put(followeeId, newUser(followeeId));
if (followerId == followeeId) return;
map.get(followerId).follow(followeeId);
 }

/**
 * Follower unfollows a followee. If the operation is invalid,
 * it should be a no-op.
 */
publicvoidunfollow(intfollowerId, intfolloweeId) {
if (!map.containsKey(followerId)) map.put(followerId, newUser(followerId));
if (!map.containsKey(followeeId)) map.put(followeeId, newUser(followeeId));
if (followerId == followeeId) return;
map.get(followerId).unfollow(followeeId);
 }

classUser {
intid;
LinkedList<Tweet> tweets = newLinkedList<>();
Set<Integer> following = newHashSet<>();
User(inti) {
id = i;
 }

publicvoidaddTweet(inti, intts) {
tweets.add(newTweet(i, ts));
while (tweets.size() > 10) {
tweets.removeFirst();
 }
 }

publicvoidfollow(intuserId) {
following.add(userId);
 }

publicvoidunfollow(intuserId) {
if (following.contains(userId)) {
following.remove(userId);
 }
 }
 }

classTweet {
intid;
inttimestamp;
Tweet(inti, intts) {
id = i;
timestamp = ts;
 }
 }
 }

/**
 * Your Twitter object will be instantiated and called as such:
 * Twitter obj = new Twitter();
 * obj.postTweet(userId,tweetId);
 * List<Integer> param_2 = obj.getNewsFeed(userId);
 * obj.follow(followerId,followeeId);
 * obj.unfollow(followerId,followeeId);
 */

}