README_EN.md

1845. Seat Reservation Manager

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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.

Solutions

Python3

class SeatManager:

    def __init__(self, n: int):
        self.q = list(range(1, n + 1))
        heapify(self.q)

    def reserve(self) -> int:
        return heappop(self.q)

    def unreserve(self, seatNumber: int) -> None:
        heappush(self.q, seatNumber)


# Your SeatManager object will be instantiated and called as such:
# obj = SeatManager(n)
# param_1 = obj.reserve()
# obj.unreserve(seatNumber)

Java

class SeatManager {
    private PriorityQueue<Integer> q = new PriorityQueue<>();

    public SeatManager(int n) {
        for (int i = 1; i <= n; ++i) {
            q.offer(i);
        }
    }

    public int reserve() {
        return q.poll();
    }

    public void unreserve(int seatNumber) {
        q.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);
 */

C++

class SeatManager {
public:
    SeatManager(int n) {
        for (int i = 1; i <= n; ++i) {
            q.push(i);
        }
    }

    int reserve() {
        int seat = q.top();
        q.pop();
        return seat;
    }

    void unreserve(int seatNumber) {
        q.push(seatNumber);
    }

private:
    priority_queue<int, vector<int>, greater<int>> q;
};

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

Go

type SeatManager struct {
	q hp
}

func Constructor(n int) SeatManager {
	q := hp{}
	for i := 1; i <= n; i++ {
		heap.Push(&q, i)
	}
	return SeatManager{q}
}

func (this *SeatManager) Reserve() int {
	return heap.Pop(&this.q).(int)
}

func (this *SeatManager) Unreserve(seatNumber int) {
	heap.Push(&this.q, seatNumber)
}

type hp struct{ sort.IntSlice }

func (h hp) Less(i, j int) bool  { return h.IntSlice[i] < h.IntSlice[j] }
func (h *hp) Push(v interface{}) { h.IntSlice = append(h.IntSlice, v.(int)) }
func (h *hp) Pop() interface{} {
	a := h.IntSlice
	v := a[len(a)-1]
	h.IntSlice = a[:len(a)-1]
	return v
}

/**
 * Your SeatManager object will be instantiated and called as such:
 * obj := Constructor(n);
 * param_1 := obj.Reserve();
 * obj.Unreserve(seatNumber);
 */

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