package datastruct

/*

栈

*/

class Stack<T> : Iterator<T>{

//stack的count

var elementCount: Int = 0

//stack内部实现为MutableList

var items: MutableList<T> = mutableListOf()

//判断Stack是否为null

fun isEmpty(): Boolean = this.items.isEmpty()

//获取statck的items count

fun count(): Int = this.items.count()

override fun toString(): String {

return this.items.toString()

}

fun push(item: T): T?{

elementCount++

items.add(item)

return item

}

//pop操作，弹出栈顶元素即链表最末端元素，可为null

fun pop(): T?{

if (this.isEmpty()){

return null

}else{

elementCount--

val item = this.items.count()-1

return this.items.removeAt(item)

}

}

//只读操作，不弹出

fun peek(): T?{

if (isEmpty()){

return null

}else{

return this.items[this.items.count() - 1]

}

}

override fun hasNext(): Boolean {

val hasNext = elementCount < count()

if (!hasNext) elementCount = 0

return hasNext

}

override fun next(): T {

if (hasNext()){

val topPos: Int = (count() - 1) - elementCount

elementCount++

return this.items[topPos]

}else{

throw NoSuchElementException("No such element")

}

}

}