# Intervals with Exactly X Concurrent Meetings Given half-open meeting intervals and an integer X, return every maximal half-open time interval during which exactly X meetings are active, restricted to the finite observation domain from the minimum meeting start through the maximum meeting end. A meeting ending at time t is not active at t, while a meeting starting at t is active. Return intervals sorted by start time and merge adjacent output intervals when the active count remains X across their boundary. If there are no meetings, return an empty list for every X. ## Function Contract Implement `intervals_with_concurrency(starts, ends, x) -> list[list[int]]`. ## Constraints - 0 <= number of meetings <= 200000. - 0 <= start < end <= 10^9 for every meeting. - 0 <= x <= number of meetings. - Zero-length output intervals must not be returned. - Spans before the minimum start and at or after the maximum end are outside the observation domain. ## Examples ```text starts = [1, 2, 4], ends = [5, 6, 7], x = 2 output = [[2, 4], [5, 6]] ``` ```text starts = [1, 5], ends = [2, 7], x = 0 output = [[2, 5]] ``` ```hint Test a shared boundary Include one meeting ending exactly when another starts and verify the half-open convention at that timestamp. ``` ```hint Exercise zero concurrency Use two separated meetings and check that only the finite gap inside the observation domain is returned when X is zero. ```