1845.seat-reservation-manager.java

class SeatManager {
    PriorityQueue<Integer> pq;
    public SeatManager(int n) {
        pq = new PriorityQueue<>();
        
        int i=1;
        while(i<=n)
            pq.offer(i++);
        
    }
    
    public int reserve() {
        return pq.poll();
    }
    
    public void unreserve(int seatNumber) {
        pq.offer(seatNumber);
    }
}

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