3433. Count Mentions Per User

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3433. Count Mentions Per User

Description

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“]

    • 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.

  2. 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:

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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:

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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:

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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]) <= 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.

Hints/Notes

Solution

Language: C++

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class Solution {
public:
    vector<int> countMentions(int numberOfUsers, vector<vector<string>>& events) {
        vector<int> res(numberOfUsers, 0);
        vector<bool> status(numberOfUsers, true);
        vector<int> hereEvent;
        vector<vector<int>> statusEvents;
        for (auto& event : events) {
            auto& type = event[0];
            int time = stoi(event[1]);
            if (type == "MESSAGE") {
                string mentions = event[2];
                if (mentions == "ALL") {
                    for (int i = 0; i < numberOfUsers; i++) {
                        res[i]++;
                    }
                } else if (mentions == "HERE") {
                    hereEvent.push_back(time);
                } else {
                    istringstream iss(mentions);
                    do {
                        string user;
                        iss >> user;
                        if (user == "") {
                            break;
                        }
                        user = user.substr(2);
                        int userId = stoi(user);
                        res[userId]++;
                    } while (iss);
                }
            } else {
                int userId = stoi(event[2]);
                statusEvents.push_back({time, userId, 1});
                statusEvents.push_back({time + 60, userId, 0});
            }
        }
        ranges::sort(hereEvent);
        ranges::sort(statusEvents);
        int j = 0;
        for (int i = 0; i < hereEvent.size(); i++) {
            int time = hereEvent[i];
            while (j < statusEvents.size() && statusEvents[j][0] <= time) {
                int userId = statusEvents[j][1];
                status[userId] = 1 - statusEvents[j][2];
                j++;
            }
            for (int k = 0; k < numberOfUsers; k++) {
                res[k] += status[k];

            }
        }
        return res;
    }
};