3433: Count Mentions Per User

Problem Statement

You are given an integer numberOfUsers representing the total number of users and an array events of size n x 3.

Each events[i] can be either of the following two types:

  1. Message Event: ["MESSAGE", "timestampi", "mentions_stringi"]
<ul>
	<li>This event indicates that a set of users was mentioned in a message at <code>timestamp<sub>i</sub></code>.</li>
	<li>The <code>mentions_string<sub>i</sub></code> string can contain one of the following tokens:
	<ul>
		<li><code>id&lt;number&gt;</code>: where <code>&lt;number&gt;</code> is an integer in range <code>[0,numberOfUsers - 1]</code>. There can be <strong>multiple</strong> ids separated by a single whitespace and may contain duplicates. This can mention even the offline users.</li>
		<li><code>ALL</code>: mentions <strong>all</strong> users.</li>
		<li><code>HERE</code>: mentions all <strong>online</strong> users.</li>
	</ul>
	</li>
</ul>
</li>
<li><strong>Offline Event:</strong> <code>[&quot;OFFLINE&quot;, &quot;timestamp<sub>i</sub>&quot;, &quot;id<sub>i</sub>&quot;]</code>
<ul>
	<li>This event indicates that the user <code>id<sub>i</sub></code> had become offline at <code>timestamp<sub>i</sub></code> for <strong>60 time units</strong>. The user will automatically be online again at time <code>timestamp<sub>i</sub> + 60</code>.</li>
</ul>
</li>

Return an array mentions where mentions[i] represents the number of mentions the user with id i has across all MESSAGE events.

All users are initially online, and if a user goes offline or comes back online, their status change is processed before handling any message event that occurs at the same timestamp.

Note that a user can be mentioned multiple times in a single message event, and each mention should be counted separately.

Example 1:

Input: numberOfUsers = 2, events = [["MESSAGE","10","id1 id0"],["OFFLINE","11","0"],["MESSAGE","71","HERE"]]

Output: [2,2]

Explanation:

Initially, all users are online.

At timestamp 10, id1 and id0 are mentioned. mentions = [1,1]

At timestamp 11, id0 goes offline.

At timestamp 71, id0 comes back online and "HERE" is mentioned. mentions = [2,2]

Example 2:

Input: numberOfUsers = 2, events = [["MESSAGE","10","id1 id0"],["OFFLINE","11","0"],["MESSAGE","12","ALL"]]

Output: [2,2]

Explanation:

Initially, all users are online.

At timestamp 10, id1 and id0 are mentioned. mentions = [1,1]

At timestamp 11, id0 goes offline.

At timestamp 12, "ALL" is mentioned. This includes offline users, so both id0 and id1 are mentioned. mentions = [2,2]

Example 3:

Input: numberOfUsers = 2, events = [["OFFLINE","10","0"],["MESSAGE","12","HERE"]]

Output: [0,1]

Explanation:

Initially, all users are online.

At timestamp 10, id0 goes offline.

At timestamp 12, "HERE" is mentioned. Because id0 is still offline, they will not be mentioned. mentions = [0,1]

Constraints:

  • 1 <= numberOfUsers <= 100
  • 1 <= events.length <= 100
  • events[i].length == 3
  • events[i][0] will be one of MESSAGE or OFFLINE.
  • 1 <= int(events[i][1]) <= 105
  • The number of id<number> mentions in any "MESSAGE" event is between 1 and 100.
  • 0 <= <number> <= numberOfUsers - 1
  • It is guaranteed that the user id referenced in the OFFLINE event is online at the time the event occurs.

Code Solution