Count Mentions Per User Leetcode 3433

December 12, 2025

Count Mentions Per User Leetcode 3433

3433. Count Mentions Per User

Solved

Medium

Topics

Companies

Hint

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:

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

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.