1845. Seat Reservation Manager

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1845. Seat Reservation Manager

Description

Difficulty: Medium

Related Topics: Design, Heap (Priority Queue)

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:

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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.

Hints/Notes

  • priority queue

Solution

Language: C++

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class SeatManager {
public:
    priority_queue<int, vector<int>, greater<int>> pq;

    SeatManager(int n) {
        for (int i = 1; i <= n; i++) {
            pq.push(i);
        }        
    }
    
    int reserve() {
        int num = pq.top();
        pq.pop();
        return num;
    }
    
    void unreserve(int seatNumber) {
        pq.push(seatNumber);
    }
};

/**
 * Your SeatManager object will be instantiated and called as such:
 * SeatManager* obj = new SeatManager(n);
 * int param_1 = obj->reserve();
 * obj->unreserve(seatNumber);
 */