grindelfStack

This is my Kotlin implementation of stack data structure

How it works?

Stack is a generic collection of elements, which is implementing the LIFO (Last-In, First-Out): when you add several items to the stack, the only way to get the first one is to exclude all the following ones. You can:

• add element to the stack,
• exclude and return the last element,
• return it without excluding,
• know if the stack is empty,
• set stack container size
• and create a new stack, containing the elements of the initial stack, on which some operation was done.

Creating an object of a Stack

Object of class "Stack" can be created using three different constructors:

1. With parameter "size": this way you create an instance of Stack of a particular length, which you pass as a parameter.
2. With parameter "collection": this way you create an instance of Stack and fill it completely with a Kotlin ArrayList you pass as a conctructor.
3. Without parameters: this way you create an instance of an empty Stack.

Stack realization

Properties (private)

1. elements: ArrayList<T?> - stack itself, realized as an instance of a Kotlin ArrayList.
2. length: Int - maximum capasity of this Stack (can be modified externally using "setSize" function).
3. upperIndex: Int - index of the topmost element of Stack (if it's equal to the size property it means, that the Stack is full).

Constructors

1. With parameter "size": checks if size is positive integer (throws an exception if otherwise) and initializes properties of the class.
2. With parameter "collection": gets a Kotlin ArrayList of data, initializes properties of the class.
3. Without parameters: initializes properties of the class (size to 0 and stack to 0 size Kotlin ArrayList). (NOTE: upperIndex property is always set to 0 value when initialized, exept for the case, when a collection of data is passed to the constructor - in this case upperIndex property is set equal to the size property.)

Functions

1. push(element: T?) - adds an element of type of the Stack to the Stack.
2. pop(): T? - removes last added element from the Stack and returns it.
3. top(): T? - returns last added element of the Stack without removing it.
4. isEmpty(): Boolean - returns true if the upperIndex property is equal to 0, otherwise - returns false.
5. setSize(value: Int) - checks if provided parameter's value is less than value of upperIndex property and if so - throws an exception, otherwise sets size property to the parameter value.
6. map(mapper: (T?) -> T?) : Stack - applies some function passed as a parameter to every element of a Stack and returns a new Stack of these updated elements.

Functions (private)

1. isMonotone(collection: ArrayList<T?>): Boolean - checks if the colection passed as a parameter is monotone (if there are any null elements, they aren't surrounded by non-null elements).
2. getUpperIndex(collection: ArrayList<T?>): Int - returns the index of the last non-null element in a row.