Stack and Queue in Swift. Generic Implementation

I already described Stack and Queue data structures and how to implement them in Swift in my previous post about stack and queue. There I used class (reference type) for implementing stack and queue, also I used them for resolve task for define that string is palindrome.

Now let's update our implementation, for now let's use struct (value type) because it is always preferable to use struct(value type) if it no need for class features (like inheritance for example).

Non generic implementation (only for Int type)

Stack Implementation

// LIFO - Last In First Out
struct Stack {
    
    var array: [Int] = []
    
    var isEmpty: Bool {
        return array.isEmpty
    }
    
    // add new element to the stack
    mutating func push(_ element: Int) {
        array.append(element)
    }
    
    // get the last element from the stack and remove it form stack
    mutating func pop() -> Int? {
        if !isEmpty {
            let value = array.removeLast()
            return value
        }
        return nil
    }
    
    // get the head of stack - the last element
    mutating func peek() -> Int? {
        if !isEmpty {
            let value = array.last
            return value
        }
        return nil
    }
}

Queue Implementation

// FIFO - First In First Out
struct Queue {
    
    var array: [Int] = []
    
    var isEmpty: Bool {
        return array.isEmpty
    }
    
    // add new element to queue
    mutating func enqueue(_ element: Int) {
        array.append(element)
    }
    
    // get the first element and remove it from queue
    mutating func dequeue() -> Int? {
        if !isEmpty {
            let value = array.removeFirst()
            return value
        }
        return nil
    }
    
    // get the head of queue - the first element
    mutating func peek() -> Int? {
        if !isEmpty {
            let value = array.first
            return value
        }
        return nil
    }
}

Here example of adding randomly generated integer number to stack and queue.

var stack = Stack()
var queue = Queue()
    
let randomNumer = Int(arc4random_uniform(100))
stack.push(randomNumer)
queue.enqueue(randomNumer)

Generic Implementation

But it is always useful to write universal solutions for our tasks. So let's implement generic versions of stack and queue.

Stack Implementation

// LIFO - Last In First Out
struct Stack<T> {
    
    var array: [T] = []
    
    var isEmpty: Bool {
        return array.isEmpty
    }
    
    // add new element to the stack
    mutating func push(_ element: T) {
        array.append(element)
    }
    
    // get the last element from the stack and remove it form stack
    mutating func pop() -> T? {
        if !isEmpty {
            let value = array.popLast()
            return value
        }
        return nil
    }
    
    // get the head of stack - the last element
    func peek() -> T? {
        if !isEmpty {
            let value = array.last
            return value
        }
        return nil
    }
    
}

Queue Implementation

// FIFO - First In First Out
struct Queue<T> {
    
    var array: [T] = []
    
    var isEmpty: Bool {
        return array.isEmpty
    }
    
    // add new element to queue
    mutating func enqueue(_ element: T) {
        array.append(element)
    }
    
    // get the first element and remove it from queue
    mutating func dequeue() -> T? {
        if !array.isEmpty {
            let value = array.removeFirst()
            return value
        }
        return nil
    }
    
    // get the head of queue - the first element
    mutating func peek() -> T? {
        if !array.isEmpty {
            let value = array.first
            return value
        }
        return nil
    }
    
}

Now we can easily use stack for any type we need. For Integer:

var stack = Stack<Int>()
var queue = Queue<Int>()
    
let randomNumer = Int(arc4random_uniform(100))
stack.push(randomNumer)
queue.enqueue(randomNumer)

Or for String

var stack = Stack<String>()
var queue = Queue<String>()

Or even for Any, in this case we can add to stack and queue String and Integer both.

var stack = Stack<Any>()
var queue = Queue<Any>()

Demo Application

Stack and Queue before the values are obtained from them

Stack and Queue after the values are obtained from them

Source Code

Source code for demo app can be found on GitHub: Stack vs Queue Demo App