1845 - Seat Reservation Manager.

Medium

Design a system that manages the reservation state of n seats that are numbered from 1 to n.

Implement the SeatManager class:

• SeatManager(int n) Initializes a SeatManager object that will manage n seats numbered from 1 to n. All seats are initially available.

• int reserve() Fetches the smallest-numbered unreserved seat, reserves it, and returns its number.

• void unreserve(int seatNumber) Unreserves the seat with the given seatNumber.

Example 1:

Input "SeatManager", "reserve", "reserve", "unreserve", "reserve", "reserve", "reserve", "reserve", "unreserve" [5, [], [], 2, [], [], [], [], 5]

Output: null, 1, 2, null, 2, 3, 4, 5, null

Explanation:

SeatManager seatManager = new SeatManager(5); // Initializes a SeatManager with 5 seats.

seatManager.reserve(); // All seats are available, so return the lowest numbered seat, which is 1.

seatManager.reserve(); // The available seats are 2,3,4,5, so return the lowest of them, which is 2.

seatManager.unreserve(2); // Unreserve seat 2, so now the available seats are 2,3,4,5.

seatManager.reserve(); // The available seats are 2,3,4,5, so return the lowest of them, which is 2.

seatManager.reserve(); // The available seats are 3,4,5, so return the lowest of them, which is 3.

seatManager.reserve(); // The available seats are 4,5, so return the lowest of them, which is 4.

seatManager.reserve(); // The only available seat is seat 5, so return 5.

seatManager.unreserve(5); // Unreserve seat 5, so now the available seats are 5.

Constraints:

• <code>1 <= n <= 10⁵</code>

• 1 <= seatNumber <= n

• For each call to reserve, it is guaranteed that there will be at least one unreserved seat.

• For each call to unreserve, it is guaranteed that seatNumber will be reserved.

• At most <code>10⁵</code> calls in total will be made to reserve and unreserve.