var array = [1, 2, 3, 4, 5]
   var set: Set = [1, 2, 3, 4, 5]
   var dictionary = ["one": 1, "two": 2, "three": 3]
   

   var name: String? = "John"
   if let unwrappedName = name {
       print("Name is \(unwrappedName)")
   }
   

   func increment(value: inout Int) {
       value += 1
   }
   var number = 1
   increment(value: &number)
   

   DispatchQueue.global(qos: .background).async {
       // Фоновая задача
       DispatchQueue.main.async {
           // Обновление UI на главном потоке
       }
   }
   

   class MyClass {
       lazy var expensiveObject: ExpensiveObject = {
           return ExpensiveObject()
       }()
   }
   

   var cache = [Int: Int]()
   func fibonacci(_ n: Int) -> Int {
       if let result = cache[n] {
           return result
       }
       if n <= 1 { return n }
       let result = fibonacci(n - 1) + fibonacci(n - 2)
       cache[n] = result
       return result
   }
   

   for i in 0..<1000 {
       // Оптимизированный код
   }
   

   struct Point {
       var x: Int
       var y: Int
   }
   

struct Stack<T> {
    private var elements: [T] = []

    mutating func push(_ item: T) {
        elements.append(item)
    }

    mutating func pop() -> T? {
        return elements.popLast() // Удаляет и возвращает верхний элемент
    }

    func peek() -> T? {
        return elements.last // Возвращает верхний элемент без удаления
    }

    func isEmpty() -> Bool {
        return elements.isEmpty
    }
}

// Пример использования:
var stack = Stack<Int>()
stack.push(10)
stack.push(20)
stack.push(30)

print(stack.pop()!) // 30
print(stack.peek()!) // 20
print(stack.isEmpty()) // false

class Person {
    weak var name: String? // ❌ Ошибка! Строки – это value type, weak нельзя
}

class Car {
    weak var model: String? // ❌ Ошибка (value type)
    weak var owner: Person? // ⚠️ Будет nil, если нет других strong ссылок
}

class Person {
    var car: Car?
}

var person: Person? = Person()
person?.car = Car()
person?.car?.owner = person // ❌ `owner` - weak, объект сразу удалится

print(person?.car?.owner) // nil, объект Person уничтожен

   protocol SomeDelegate: AnyObject {
       func doSomething()
   }

   class ViewController {
       weak var delegate: SomeDelegate? // ✅ Prevent retain cycle
   }

struct Car {
    var model: String
    var year: Int

    func description() -> String {
        return "\(model) – \(year)"
    }
}

let car1 = Car(model: "Tesla", year: 2023)
var car2 = car1 // Создается копия

print(car1.description()) // Tesla – 2023
print(car2.description()) // Tesla – 2023

car2.year = 2024 // Изменяем car2, но car1 остается прежним
print(car1.year) // 2023
print(car2.year) // 2024

struct Counter {
    var count = 0

    mutating func increment() {
        count += 1
    }
}

var counter = Counter()
counter.increment()
print(counter.count) // 1

struct Stack<Element> {
    private var storage: [Element] = []

    mutating func push(_ element: Element) {
        storage.append(element)
    }

    mutating func pop() -> Element? {
        return storage.popLast()
    }

    func peek() -> Element? {
        return storage.last
    }

    var isEmpty: Bool {
        return storage.isEmpty
    }
}

class Node<Element> {
    var value: Element
    var next: Node?

    init(value: Element) {
        self.value = value
    }
}

struct Stack<Element> {
    private var head: Node<Element>?

    mutating func push(_ element: Element) {
        let node = Node(value: element)
        node.next = head
        head = node
    }

    mutating func pop() -> Element? {
        let node = head
        head = head?.next
        return node?.value
    }

    func peek() -> Element? {
        return head?.value
    }

    var isEmpty: Bool {
        return head == nil
    }
}

struct Person: Hashable {
    let id: Int
    let name: String
}

// Теперь можно использовать `Person` как ключ
var peopleAges: [Person: Int] = [
    Person(id: 1, name: "Alice"): 25,
    Person(id: 2, name: "Bob"): 30
]

// Доступ по ключу
let alice = Person(id: 1, name: "Alice")
print(peopleAges[alice] ?? "Не найдено") // 25

struct Person: Hashable {
    let id: Int
    let name: String

    func hash(into hasher: inout Hasher) {
        hasher.combine(id)   // Используем только id для хеша
    }
}

let newVC = UIViewController()
present(newVC, animated: true)

dismiss(animated: true)

// Открываем два экрана последовательно
let vc1 = UIViewController()
let vc2 = UIViewController()
present(vc1, animated: true) 
vc1.present(vc2, animated: true)

vc2.dismiss(animated: true)

vc1.dismiss(animated: true)

let vc1 = UIViewController()
let vc2 = UIViewController()
navigationController?.pushViewController(vc1, animated: true)
navigationController?.pushViewController(vc2, animated: true)

vc2.dismiss(animated: true)

navigationController?.popViewController(animated: true)

navigationController?.popToRootViewController(animated: true)