Count Mentions Per User

arraymathsorting

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:

Message Event: ["MESSAGE", "timestamp _i ", "mentions_string _i "]

This event indicates that a set of users was mentioned in a message at timestamp _i .

The mentions_string _i 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", "timestamp _i ", "id _i "]

This event indicates that the user id _i had become offline at timestamp _i for 60 time units . The user will automatically be online again at time timestamp _i + 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 .

Examples

Example 1

Input: numberOfUsers = 2, events = [["MESSAGE","10","id1 id0"],["OFFLINE","11","0"],["MESSAGE","71","HERE"]]
Output: [2,2]
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]
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]
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]) <= 10 ^5

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.

🤔

Medium

Difficulty

Topic Info

ModuleDSA

CategoryArray

Sub-topicMath