<p>Design a simplified version of Twitter where users can post tweets, follow/unfollow another user, and is able to see the <code>10</code> most recent tweets in the user&#39;s news feed.</p>

<p>Implement the <code>Twitter</code> class:</p>

<ul>
	<li><code>Twitter()</code> Initializes your twitter object.</li>
	<li><code>void postTweet(int userId, int tweetId)</code> Composes a new tweet with ID <code>tweetId</code> by the user <code>userId</code>. Each call to this function will be made with a unique <code>tweetId</code>.</li>
	<li><code>List&lt;Integer&gt; getNewsFeed(int userId)</code> Retrieves the <code>10</code> most recent tweet IDs in the user&#39;s news feed. Each item in the news feed must be posted by users who the user followed or by the user themself. Tweets must be <strong>ordered from most recent to least recent</strong>.</li>
	<li><code>void follow(int followerId, int followeeId)</code> The user with ID <code>followerId</code> started following the user with ID <code>followeeId</code>.</li>
	<li><code>void unfollow(int followerId, int followeeId)</code> The user with ID <code>followerId</code> started unfollowing the user with ID <code>followeeId</code>.</li>
</ul>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input</strong>
[&quot;Twitter&quot;, &quot;postTweet&quot;, &quot;getNewsFeed&quot;, &quot;follow&quot;, &quot;postTweet&quot;, &quot;getNewsFeed&quot;, &quot;unfollow&quot;, &quot;getNewsFeed&quot;]
[[], [1, 5], [1], [1, 2], [2, 6], [1], [1, 2], [1]]
<strong>Output</strong>
[null, null, [5], null, null, [6, 5], null, [5]]

<strong>Explanation</strong>
Twitter twitter = new Twitter();
twitter.postTweet(1, 5); // User 1 posts a new tweet (id = 5).
twitter.getNewsFeed(1);  // User 1&#39;s news feed should return a list with 1 tweet id -&gt; [5]. return [5]
twitter.follow(1, 2);    // User 1 follows user 2.
twitter.postTweet(2, 6); // User 2 posts a new tweet (id = 6).
twitter.getNewsFeed(1);  // User 1&#39;s news feed should return a list with 2 tweet ids -&gt; [6, 5]. Tweet id 6 should precede tweet id 5 because it is posted after tweet id 5.
twitter.unfollow(1, 2);  // User 1 unfollows user 2.
twitter.getNewsFeed(1);  // User 1&#39;s news feed should return a list with 1 tweet id -&gt; [5], since user 1 is no longer following user 2.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= userId, followerId, followeeId &lt;= 500</code></li>
	<li><code>0 &lt;= tweetId &lt;= 10<sup>4</sup></code></li>
	<li>All the tweets have <strong>unique</strong> IDs.</li>
	<li>At most <code>3 * 10<sup>4</sup></code> calls will be made to <code>postTweet</code>, <code>getNewsFeed</code>, <code>follow</code>, and <code>unfollow</code>.</li>
</ul>