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iOS

Posted by Joyce Ryu
Joyce Ryu
1,124 Points

About Queue and Stack - do we have lectures on this topic?

I am taking iOS swift development course, and looking for Queue and Stack problem solving but cannot find one. In teamtreehouse, do we lectures on this ? If there is, what course can I find it?

1 Answer

Richard Lu
Richard Lu
20,185 Points

Hi Hee Eun,

What I understand is that you're looking for a course to learn more about the Queue/Stack data structure in Swift, and from my knowledge I don't think there is one.

The problem with Swift using the queue/stack data structure is that there isn't an actual struct like an array (yes, I mean struct). The good news is you can easily build them!

Here's a generic stack implementation with the push and pop capabilities. 

struct Stack<T> {
    private var stack = [T]()

    mutating func push(newElement: T) {
        stack.append(newElement)
    }

    mutating func pop() -> T? {
        return stack.popLast()
    }

    func peek() -> T? {
        return stack.last
    }
}

Here's a generic queue implementation.

struct Queue<T> {
    private var queue = [T]()

    mutating func add(newElement: T) {
        queue.append(newElement)
    }

    mutating func remove() -> T? {
        return queue.count > 0 ? queue.removeFirst() : nil
    }

    func peek() -> T? {
        return queue.first
    }
}

If you'd like me to break down what the code is doing please let me know. Good luck. Happy coding! :)

Joyce Ryu
Joyce Ryu
1,124 Points

Wow I didn't expect this much! Thank you very much !

Joyce Ryu
Joyce Ryu
1,124 Points

'''html

struct Stack {

}

var newStack = Stack()
newStack.push("HistoryListController")
newStack.push("HistoryDetailViewController")
newStack.push("HistoryTimelineViewController")
newStack.push("HistoryChartViewController")

if let topVC = newStack.topItem {
    print("Top View Controller is \(topVC)")
    //HistoryChartViewController
}

newStack.pop()

if let topVC = newStack.topItem {
    print("Top View Controller is \(topVC)")
    //HistoryTimelineViewController
} '''

Is this right way to make stack coding?

Richard Lu
Richard Lu
20,185 Points

Hi Hee Eun,

Your code is close to correct if you just want to mimic the behavior of what's going on with UIViewControllers using strings. Using the stack that I've provided above, you must provide a type.

var newStack = Stack<String>()

to find the top item in your stack, I've implemented it as the method 'peek'

if let topVC = newStack.peek() {
    print("Top View Controller is \(topVC)")
    //HistoryChartViewController
}
Joyce Ryu
Joyce Ryu
1,124 Points

Can you write whole codes using what I posted below?? I get all rows error

Richard Lu
Richard Lu
20,185 Points

Hi Hee Eun,

Sorry for the delay in response. Here's your code written out to be compatible for Swift 2.0.

struct Stack<T> {
    private var stack = [T]()

    mutating func push(newElement: T) {
        stack.append(newElement)
    }

    mutating func pop() -> T? {
        return stack.popLast()
    }

    func peek() -> T? {
        return stack.last
    }
}

var newStack = Stack<String>()
newStack.push("HistoryListController")
newStack.push("HistoryDetailViewController")
newStack.push("HistoryTimelineViewController")
newStack.push("HistoryChartViewController")

if let topVC = newStack.peek() {
    print("Top View Controller is \(topVC)")
    //HistoryChartViewController
}

newStack.pop()

if let topVC = newStack.peek() {
    print("Top View Controller is \(topVC)")
    //HistoryTimelineViewController
}