如何在0停止倒计时？-- Swift

import UIKit

class ViewController: UIViewController {
    var timer: Timer?
    var count = 10
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        startCountdown()
    }
    
    func startCountdown() {
        timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(updateCountdown), userInfo: nil, repeats: true)
    }
    
    @objc func updateCountdown() {
        count -= 1
        print(count)
        
        if count == 0 {
            stopCountdown()
        }
    }
    
    func stopCountdown() {
        timer?.invalidate()
        timer = nil
        print("倒计时结束")
    }
}