Stack notes - incomplete implementation [MARKED FOR DELETION]

Stack-In-class-notes.swift

//
//  main.swift
//  Stack
//
//  Created by Alex Paul on 10/6/20.
//

import Foundation

struct Stack<T> {
  // private(set) public var allows access but not modification outside the LinkedList
  private(set) public var elements = [T]()
}


// implement a stack using a linked list

// 1.
// create a node class that uses a double node
// ADT

// review: memory management, ARC, weak, strong, unowned
// [newObject retain]; // 1
// [newObject release]; // 0
// reference counting: is the OS managing the reference contains in the lifetime of an application
// init() - create objects
// deint() - called automatically when an object is destroyed
//         - deint() won't get called if the object is in a retain cycle


class DLNode<T> {
  // node has at minimum a value and a next pointer (references)
  var value: T // no value exist
  var next: DLNode<T>? // by default var is a strong reference
  weak var previous: DLNode<T>?
  init(_ value: T) { // 8
    // ourValue = 8
    self.value = value // 8
  }
}

// node1 <-> node2 -> nil


// 2.
// create a linked list
// at minimun implement the following
// properties and functions
// count, isEmpty, peek
// append(), removeLast()
// extra: insert, replaceHead

// ADT
struct LinkedList<T> {
  
  // data structure
  private var head: DLNode<T>?
  private var tail: DLNode<T>?
  
  // could only get (retrieve) the value externally
  // can mutate the value internally
  private (set) public var count = 0
  
  public var isEmpty: Bool {
    return head == nil
  }
  
  // 1 -> 2 -> 3 -> nil
  public var peek: T? {
    return tail?.value
  }
  
}

// 3.
// implement a stack using a linked list