---
# System prepended metadata

title: 1845. Seat Reservation Manager
tags: [LeetCode Medium, LeetCode Study Group - Heap, Prep Again, LeetCode Study Group]

---

###### tags: `LeetCode Study Group - Heap` `LeetCode Medium` `LeetCode Study Group` `Prep Again`
# 1845. Seat Reservation Manager
Link: https://leetcode.com/problems/seat-reservation-manager/description/

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

Time Complexity: O(nlogn)
Space Complexity: O(n)

  ``` java

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

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

## Reference
https://leetcode.com/problems/seat-reservation-manager/solutions/2816403/java-extremely-easy-code-with-explanation/