Stack is an abstract data type that serves as a collection of elements, with two principal operations: push, which adds an element to the collection, and pop, which removes the most recently added element that was not yet removed. The order in which elements come off a stack gives rise to its alternative name, LIFO (for last in, first out). Additionally, a peek operation may give access to the top without modifying the stack.
class Stack<T:Comparable<T>>(list:MutableList<T>) { var items: MutableList<T> = list fun isEmpty():Boolean = this.items.isEmpty() fun count():Int = this.items.count() fun push(element:T) { val position = this.count() this.items.add(position, element) } override fun toString() = this.items.toString() fun pop():T? { if (this.isEmpty()) { return null } else { val item = this.items.count() - 1 return this.items.removeAt(item) } } fun peek():T? { if (isEmpty()) { return null } else { return this.items[this.items.count() - 1] } } }