LeetCode in Kotlin

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:

• 1 <= n <= 105
• 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 105 calls in total will be made to reserve and unreserve.

Solution

import java.util.PriorityQueue
import java.util.Queue

@Suppress("UNUSED_PARAMETER")
class SeatManager(n: Int) {
    private val seats: Queue<Int>
    private var smallest: Int

    init {
        seats = PriorityQueue()
        smallest = 0
    }

    fun reserve(): Int {
        return if (seats.isEmpty()) ++smallest else seats.poll()
    }

    fun unreserve(seatNumber: Int) {
        seats.offer(seatNumber)
    }
}

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