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3721. Count Mentions Per User

Array Math Sorting Simulation

Problem - Count Mentions Per User

Medium

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:

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.

Solutions

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class Solution:
    def countMentions(self, numberOfUsers: int, events: List[List[str]]) -> List[int]:
        events.sort(key=lambda x: (int(x[1]), x[0][2]))
        all_mentions = 0
        result = [0] * numberOfUsers
        online = [0] * numberOfUsers

        for msg_type, time, val in events:
            current = int(time)
            if msg_type[0] == "O":
                online[int(val)] = current + 60
            elif val[0] == "A":
                all_mentions += 1
            elif val[0] == "H":
                for i, t in enumerate(online):
                    if t <= current:
                        result[i] += 1
            else:
                for char in val.split():
                    result[int(char[2:])] += 1
        if all_mentions:
            for i in range(numberOfUsers):
                result[i] += all_mentions
        return result

Submission Stats:

  • Runtime: 35 ms (95.47%)
  • Memory: 17.8 MB (95.09%)