type Node struct {
	key   int
	value int
}
type LRUCache struct {
	capacity int
	list     *list.List 
	mp       map[int]*list.Element // 注意1：value是list.Element
}
func Constructor(capacity int) LRUCache {
	return LRUCache{
		capacity: capacity,
		list:     list.New(),
		mp:       make(map[int]*list.Element),
	}
}
func (this *LRUCache) Get(key int) int {
	if v, ok := this.mp[key]; ok {
		this.list.MoveToFront(v)
		return v.Value.(*Node).value // 注意2：list.Element里面有一個Value any字段，所以需要斷言
	}
	return -1
}
func (this *LRUCache) Put(key int, value int) {
	if v, ok := this.mp[key]; ok {
		v.Value.(*Node).value = value
		this.list.MoveToFront(v) // 注意3：需要移動，LRU
        return
	}
	node := &Node{key, value}
	a := this.list.PushFront(node)
	this.mp[key] = a // 注意4：一定把插入鏈表的kv，也加入到哈希表
	if this.list.Len() > this.capacity { // 注意5：判斷是否越界
		tmp := this.list.Back()
		delete(this.mp, tmp.Value.(*Node).key) // 注意6：刪除已經(jīng)淘汰的數(shù)據(jù)的key
		this.list.Remove(tmp)
	}
}

type List struct {
	root Element // sentinel list element, only &root, root.prev, and root.next are used
	len  int     // current list length excluding (this) sentinel element
}

type Element struct {
	next, prev *Element
	list *List
	Value any
}

func main() {
	l := list.New()
	fmt.Printf("%+v\n",l)
}

func main() {
	l := list.New()
	l.PushBack(123)
	l.PushBack("nihao")
	l.PushFront("你好")
	l.PushFront(3.1415926)
	// 遍歷
	for e := l.Front(); e != nil; e = e.Next() {
		fmt.Printf("%+v\n", e)
	}
}

func main() {
	l := list.New()
	l.PushBack("nihao")
	a:=l.Remove(l.Back())
	fmt.Println(a)
}

func main() {
    l := list.New()
    l.PushBack(1)
    l.PushBack(2)
    l.PushBack(3)
    // 從前往后遍歷
    for e := l.Front(); e != nil; e = e.Next() {
        fmt.Println(e.Value)
    }
    // 從后往前遍歷
    for e := l.Back(); e != nil; e = e.Prev() {
        fmt.Println(e.Value)
    }
}

func main() {
    l := list.New()
    l.PushBack(1)
    l.PushBack(2)
    l.PushBack(3)
    fmt.Println(l.Len()) // 輸出: 3
}

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package list implements a doubly linked list.
//
// To iterate over a list (where l is a *List):
//
//	for e := l.Front(); e != nil; e = e.Next() {
//		// do something with e.Value
//	}
package list
// Element is an element of a linked list.
type Element struct {
	//雙鏈表元素中的下一個和上一個指針。
	//為了簡化實(shí)現(xiàn)，在內(nèi)部實(shí)現(xiàn)了列表l
	//作為一個環(huán)，這樣&l.root既是最后一個元素的下一個元素
	//list元素（l.Back（））和第一個列表的前一個元素
	//元素（l.Front（））。
	next, prev *Element
	// The list to which this element belongs.
	list *List
	// The value stored with this element.
	Value any
}
// Next returns the next list element or nil.
func (e *Element) Next() *Element {
	if p := e.next; e.list != nil && p != &e.list.root {
		return p
	}
	return nil
}
// Prev returns the previous list element or nil.
func (e *Element) Prev() *Element {
	if p := e.prev; e.list != nil && p != &e.list.root {
		return p
	}
	return nil
}
// List represents a doubly linked list.
// The zero value for List is an empty list ready to use.
type List struct {
	root Element // sentinel list element, only &root, root.prev, and root.next are used
	len  int     // current list length excluding (this) sentinel element
}
// Init initializes or clears list l.
func (l *List) Init() *List {
	l.root.next = &l.root
	l.root.prev = &l.root
	l.len = 0
	return l
}
// New returns an initialized list.
func New() *List { return new(List).Init() }
// Len returns the number of elements of list l.
// The complexity is O(1).
func (l *List) Len() int { return l.len }
// Front returns the first element of list l or nil if the list is empty.
func (l *List) Front() *Element {
	if l.len == 0 {
		return nil
	}
	return l.root.next
}
// Back returns the last element of list l or nil if the list is empty.
func (l *List) Back() *Element {
	if l.len == 0 {
		return nil
	}
	return l.root.prev
}
// lazyInit lazily initializes a zero List value.
func (l *List) lazyInit() {
	if l.root.next == nil {
		l.Init()
	}
}
// insert inserts e after at, increments l.len, and returns e.
func (l *List) insert(e, at *Element) *Element {
	e.prev = at
	e.next = at.next
	e.prev.next = e
	e.next.prev = e
	e.list = l
	l.len++
	return e
}
// insertValue is a convenience wrapper for insert(&Element{Value: v}, at).
func (l *List) insertValue(v any, at *Element) *Element {
	return l.insert(&Element{Value: v}, at)
}
// remove removes e from its list, decrements l.len
func (l *List) remove(e *Element) {
	e.prev.next = e.next
	e.next.prev = e.prev
	e.next = nil // avoid memory leaks
	e.prev = nil // avoid memory leaks
	e.list = nil
	l.len--
}
// move moves e to next to at.
func (l *List) move(e, at *Element) {
	if e == at {
		return
	}
	e.prev.next = e.next
	e.next.prev = e.prev
	e.prev = at
	e.next = at.next
	e.prev.next = e
	e.next.prev = e
}
// Remove removes e from l if e is an element of list l.
// It returns the element value e.Value.
// The element must not be nil.
func (l *List) Remove(e *Element) any {
	if e.list == l {
		// if e.list == l, l must have been initialized when e was inserted
		// in l or l == nil (e is a zero Element) and l.remove will crash
		l.remove(e)
	}
	return e.Value
}
// PushFront inserts a new element e with value v at the front of list l and returns e.
func (l *List) PushFront(v any) *Element {
	l.lazyInit()
	return l.insertValue(v, &l.root)
}
// PushBack inserts a new element e with value v at the back of list l and returns e.
func (l *List) PushBack(v any) *Element {
	l.lazyInit()
	return l.insertValue(v, l.root.prev)
}
// InsertBefore inserts a new element e with value v immediately before mark and returns e.
// If mark is not an element of l, the list is not modified.
// The mark must not be nil.
func (l *List) InsertBefore(v any, mark *Element) *Element {
	if mark.list != l {
		return nil
	}
	// see comment in List.Remove about initialization of l
	return l.insertValue(v, mark.prev)
}
// InsertAfter inserts a new element e with value v immediately after mark and returns e.
// If mark is not an element of l, the list is not modified.
// The mark must not be nil.
func (l *List) InsertAfter(v any, mark *Element) *Element {
	if mark.list != l {
		return nil
	}
	// see comment in List.Remove about initialization of l
	return l.insertValue(v, mark)
}
// MoveToFront moves element e to the front of list l.
// If e is not an element of l, the list is not modified.
// The element must not be nil.
func (l *List) MoveToFront(e *Element) {
	if e.list != l || l.root.next == e {
		return
	}
	// see comment in List.Remove about initialization of l
	l.move(e, &l.root)
}
// MoveToBack moves element e to the back of list l.
// If e is not an element of l, the list is not modified.
// The element must not be nil.
func (l *List) MoveToBack(e *Element) {
	if e.list != l || l.root.prev == e {
		return
	}
	// see comment in List.Remove about initialization of l
	l.move(e, l.root.prev)
}
// MoveBefore moves element e to its new position before mark.
// If e or mark is not an element of l, or e == mark, the list is not modified.
// The element and mark must not be nil.
func (l *List) MoveBefore(e, mark *Element) {
	if e.list != l || e == mark || mark.list != l {
		return
	}
	l.move(e, mark.prev)
}
// MoveAfter moves element e to its new position after mark.
// If e or mark is not an element of l, or e == mark, the list is not modified.
// The element and mark must not be nil.
func (l *List) MoveAfter(e, mark *Element) {
	if e.list != l || e == mark || mark.list != l {
		return
	}
	l.move(e, mark)
}
// PushBackList inserts a copy of another list at the back of list l.
// The lists l and other may be the same. They must not be nil.
func (l *List) PushBackList(other *List) {
	l.lazyInit()
	for i, e := other.Len(), other.Front(); i > 0; i, e = i-1, e.Next() {
		l.insertValue(e.Value, l.root.prev)
	}
}
// PushFrontList inserts a copy of another list at the front of list l.
// The lists l and other may be the same. They must not be nil.
func (l *List) PushFrontList(other *List) {
	l.lazyInit()
	for i, e := other.Len(), other.Back(); i > 0; i, e = i-1, e.Prev() {
		l.insertValue(e.Value, &l.root)
	}
}