You are given: - A list of log entries `logs`, where each entry is a string in the format: ``` "userId action timestamp" ``` - `userId` is a non-empty string without spaces (e.g., `"u1"`). - `action` is either `"signin"` or `"signout"`. - `timestamp` is an integer representing time in seconds. - An integer `maxTime`. A **session** for a user is defined as a pair of actions: - A `"signin"` log for that user at time `t_in`, and - The **next** `"signout"` log for the same user at time `t_out` such that `t_out > t_in`, - And that `signout` has not already been paired with a previous `signin` for that user. A session is **valid** if: ```text (t_out - t_in) <= maxTime ``` Your task is to: > Return the set (or list) of all `userId`s that have **at least one** valid session. Additional details and assumptions: - The `logs` list may **not** be sorted by time; you should handle that. - Each log belongs to exactly one user, determined by `userId`. - If there is a `signout` without any earlier unmatched `signin` for that user, ignore that `signout`. - If there is a `signin` without any later `signout`, it does not form a session. - A single user may have multiple sessions; if **any one** of them is valid, that user should be included in the output. - The output can be in any order. **Example** ```text logs = [ "u1 signin 1", "u2 signin 2", "u1 signout 5", "u2 signout 20", "u1 signin 30", "u1 signout 35" ] maxTime = 10 ``` - For `u1`: - Session 1: signin at 1, signout at 5 → duration 4 (valid) - Session 2: signin at 30, signout at 35 → duration 5 (valid) - For `u2`: - Session 1: signin at 2, signout at 20 → duration 18 (invalid if `maxTime = 10`) So the output should include `"u1"` (has valid sessions) and exclude `"u2"`. Implement a function that, given `logs` and `maxTime`, returns all such `userId`s.