golang实现栈操作

栈是限制插入和删除只能在一个位置上进行的表，该位置是表的末端，叫做栈顶。
栈有时又叫LIFO(先进后出)表。
对栈的操作有Push(进栈)和Pop(出栈)，前者相当于插入，后者相当于删除最后插入的元素。

以下用双向链表和切片实现分别实现栈操作

//stack
//用双向链表实现stack
type Element interface {}


var header *entry  //链表表头
var size int  //栈的长度

type entry struct {
	previous *entry
	next     *entry
	element  Element
}

func newEntry(prev,next *entry,e Element) *entry {
	return  &entry{prev,next,e}
}

//初始化header  表头
func NewStack() *entry {
	header = newEntry(nil,nil,nil)
	header.previous =header
	header.next = header
	return header
}

type Stack interface {
	Push(e Element)    //向栈顶添加元素
	Pop()   Element    //移除栈顶元素
	Top()   Element   //获取栈顶元素（不删除）
	Clear()  bool       //清空栈
	Size()  int            //获取栈的元素个数
	IsEmpty() bool   //判断栈是否是空栈
}

//向栈顶添加元素
func (e *entry) Push(element Element)  {
	addBefore(header,element)
}

//移除栈顶元素
func (e *entry) Pop() Element {
	if e.IsEmpty() {
		fmt.Println("stack is empty!")
		return nil
	}
	prevEntry := header.previous

	prevEntry.previous.next = header
	header.previous = prevEntry.previous

	size--
	return prevEntry.element
}

//获取栈顶元素（不删除）
func (e *entry) Top() Element {
	if e.IsEmpty() {
		fmt.Println("stack is empty!")
		return nil
	}
	return header.previous.element
}

//清空栈
func (e *entry) Clear() bool {
	if e.IsEmpty() {
		fmt.Println("stack is empty!")
		return false
	}
	entry := header.next
	for entry != header {
		nextEntry := entry.next
		entry.next = nil
		entry.previous = nil
		entry.element = nil
		entry = nextEntry
	}
	header.next = header
	header.previous = header
	size =0
	return true
}

func (e *entry) Size() int  {
	return size
}

func (e *entry) IsEmpty() bool {
	if size == 0 {
		return true
	}

	return false
}


//在entry节点之前添加
func addBefore(e *entry,element Element) Element{
	newEntry := newEntry(e.previous,e,element)
	newEntry.previous.next = newEntry
	newEntry.next.previous = newEntry
	size++
	return newEntry
}




//****************************************
//****************************************
//用切片实现Stack
type  sliceEntry struct{
	element []Element
}

func NewSliceEntry() *sliceEntry {
	return &sliceEntry{}
}

func (entry *sliceEntry)Push(e Element) {
	entry.element = append(entry.element,e)
}

func  (entry *sliceEntry)Pop() Element {
	size := entry.Size()
	if size == 0 {
		fmt.Println("stack is empty!")
		return nil
	}
	lastElement := entry.element[size-1]
	entry.element[size-1] = nil
	entry.element  = entry.element[:size-1]
	return lastElement
}

func  (entry *sliceEntry)Top() Element {
	size := entry.Size()
	if size == 0 {
		fmt.Println("stack is empty!")
		return nil
	}
	return entry.element[size-1]
}


func  (entry *sliceEntry)Clear() bool {
	if entry.IsEmpty() {
		fmt.Println("stack is empty!")
		return false
	}
	for i :=0;i<entry.Size();i++ {
		entry.element[i] = nil
	}
	entry.element = make([]Element,0)
	return true
}

func  (entry *sliceEntry)Size() int {
	return len(entry.element)
}

func  (entry *sliceEntry)IsEmpty() bool {
	if len(entry.element) == 0 {
		return true
	}
	return false
}


func main() {
	test1()
}

//测试双向链表实现的Stack
func test1() {
	stack := NewStack()
	for i := 0;i<50;i++ {
		stack.Push(i)
	}
	fmt.Println(stack.Top())
	fmt.Println(stack.Size())
	fmt.Println(stack.Pop())
	fmt.Println(stack.Top())
	fmt.Println(stack.Clear())
	fmt.Println(stack.IsEmpty())
	for i := 0;i<50;i++ {
		stack.Push(i)
	}

	fmt.Println(stack.Top())
}

//测试切片实现的Stack
func test2() {
	entry := NewSliceEntry()
	for i:= 0;i<50;i++ {
		entry.Push(i)
	}
	fmt.Println(entry.Size())
	fmt.Println(entry.Top())
	fmt.Println(entry.Pop())
	fmt.Println(entry.Top(),entry.Size())
	fmt.Println(entry.Clear())
	for i:= 0;i<50;i++ {
		entry.Push(i)
	}
	fmt.Println(entry.Size())
}

//两种方法性能比较
func test3() {
	t := time.Now()
	sliceStack := NewSliceEntry()
	for i:= 0;i<500000;i++ {
		sliceStack.Push(i)
	}
	fmt.Println(time.Since(t))




	t = time.Now()
	stack := NewStack()
	for i:=0;i<500000;i++ {
		stack.Push(i)
	}
	fmt.Println(time.Since(t))
}