SeatReservationManager.cpp

// Source : https://leetcode.com/problems/seat-reservation-manager/
// Author : Hao Chen
// Date   : 2021-05-03

/***************************************************************************************************** 
 *
 * 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 <= 10^5
 * 	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 10^5 calls in total will be made to reserve and unreserve.
 ******************************************************************************************************/

class SeatManager {
private:
    set<int> idle;
public:
    SeatManager(int n) {
        for(int i=1; i<=n; i++) {
            idle.insert(i);
        }
    }
    
    int reserve() {
        auto it = idle.begin();
        auto seat = *it;
        idle.erase(it);
        return seat;
    }
    
    void unreserve(int seatNumber) {
        idle.insert(seatNumber);
    }
};

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