Count Mentions Per User · Interview Problem

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Leetcode

Medium

Arrays

Hash Maps

Sorting

Simulation

Input Format

The first input describes the users involved.
The second input describes a list of events, each with a timestamp and a message or action type.
Each event may mention one user, multiple users, all users, or all currently active users depending on its type.
Events should be processed in increasing timestamp order, and ties should be handled consistently by the event ordering rules.

Output Format

Return an integer array where the $i$ -th value is the number of mentions received by user $i$ .
The result should include every user exactly once, in increasing user id order.

Constraints

$1 \le n \le 10^5$
Event timestamps are within a sortable integer range.
User ids are contiguous or otherwise indexable.
The solution should be efficient enough to process all events in roughly linear or $n \log n$ time, depending on ordering requirements.

Examples

Sample cases returned by the problem API.

Example 1

Input

users = 3
entries = [
  [1, "MESSAGE", [0, 2]],
  [2, "ALL", []],
  [3, "MESSAGE", [1]],
  [4, "ACTIVE", [0, 1, 2]]
]

Output

[2, 2, 2]

Explanation

User 0 is mentioned in the first message and by the ACTIVE event. User 1 is mentioned in the third message and by the ACTIVE event. User 2 is mentioned in the first message and by the ALL event.

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