Find users with at least one valid session

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:

(t_out - t_in) <= maxTime

Your task is to:

Return the set (or list) of all userIds 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

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 userIds.