在 Go 語言中，container/list 包提供了一個雙向鏈表的實現。鏈表是一種常見的數據結構，適用于頻繁插入和刪除操作的場景。container/list 包中的鏈表是雙向的，意味著每個元素都包含指向前一個和后一個元素的指針。

力扣：146. LRU 緩存

力扣算法鏈接：https://leetcode.cn/problems/lru-cache/?envType=study-plan-v2&envId=top-100-liked

請你設計并實現一個滿足 LRU (最近最少使用) 緩存 約束的數據結構。
實現 LRUCache 類：
LRUCache(int capacity) 以 正整數 作為容量 capacity 初始化 LRU 緩存。
int get(int key) 如果關鍵字 key 存在于緩存中，則返回關鍵字的值，否則返回 -1 。
void put(int key, int value) 如果關鍵字 key 已經存在，則變更其數據值 value ；如果不存在，則向緩存中插入該組 key-value 。如果插入操作導致關鍵字數量超過 capacity ，則應該 逐出 最久未使用的關鍵字。

函數 get 和 put 必須以 O(1) 的平均時間復雜度運行。

輸入
[“LRUCache”, “put”, “put”, “get”, “put”, “get”, “put”, “get”, “get”, “get”]
[[2], [1, 1], [2, 2], [1], [3, 3], [2], [4, 4], [1], [3], [4]]

輸出
[null, null, null, 1, null, -1, null, -1, 3, 4]

解釋
LRUCache lRUCache = new LRUCache(2);
lRUCache.put(1, 1); // 緩存是 {1=1}
lRUCache.put(2, 2); // 緩存是 {1=1, 2=2}
lRUCache.get(1); // 返回 1
lRUCache.put(3, 3); // 該操作會使得關鍵字 2 作廢，緩存是 {1=1, 3=3}
lRUCache.get(2); // 返回 -1 (未找到)
lRUCache.put(4, 4); // 該操作會使得關鍵字 1 作廢，緩存是 {4=4, 3=3}
lRUCache.get(1); // 返回 -1 (未找到)
lRUCache.get(3); // 返回 3
lRUCache.get(4); // 返回 4

代碼案例：

type Node struct {key   intvalue int
}type LRUCache struct {capacity intlist     *list.Listmp       map[int]*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}return -1
}func (this *LRUCache) Put(key int, value int) {if v, ok := this.mp[key]; ok {v.Value.(*Node).value = valuethis.list.MoveToFront(v)return}node := &Node{key, value}a := this.list.PushFront(node)this.mp[key] = aif this.list.Len() > this.capacity {tmp := this.list.Back()delete(this.mp, tmp.Value.(*Node).key)this.list.Remove(tmp)}
}

主要結構 List 和 Element

• List: 表示一個雙向鏈表。

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

• Element: 表示鏈表中的一個元素。

type Element struct {next, prev *Elementlist *ListValue any
}

常用方法

1. 初始化鏈表

使用 list.New() 創建一個新的鏈表。

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

2. 插入元素

• PushBack(value interface{}) *Element: 在鏈表尾部插入一個元素。
• PushFront(value interface{}) *Element: 在鏈表頭部插入一個元素。
• InsertBefore(value interface{}, mark *Element) *Element: 在指定元素前插入一個元素。
• InsertAfter(value interface{}, mark *Element) *Element: 在指定元素后插入一個元素。

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)}
}

通過運行結果可以發現，list其實就是一個環形的雙向鏈表。

3. 刪除元素

• Remove(e *Element) interface{}: 刪除鏈表中的指定元素。

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

4. 遍歷鏈表

• Front() *Element: 返回鏈表的第一個元素。
• Back() *Element: 返回鏈表的最后一個元素。
• Next() *Element: 返回當前元素的下一個元素。
• Prev() *Element: 返回當前元素的前一個元素。

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)}
}

5. 獲取鏈表長度

• Len() int: 返回鏈表中元素的個數。

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

使用場景

• 頻繁插入和刪除: 鏈表在插入和刪除操作上比數組更高效，尤其是在中間位置。
• 實現隊列和棧: 鏈表可以用來實現隊列（FIFO）和棧（LIFO）等數據結構。
• 動態數據存儲: 當數據量不確定或需要動態調整時，鏈表是一個很好的選擇。

注意事項

• 內存開銷: 鏈表的每個元素都需要額外的內存來存儲前后指針，因此內存開銷比數組大。
• 隨機訪問性能差: 鏈表不支持隨機訪問，訪問某個元素需要從頭或尾開始遍歷。

源代碼閱讀

// 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。//為了簡化實現，在內部實現了列表l//作為一個環，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 usedlen  int     // current list length excluding (this) sentinel element
}// Init initializes or clears list l.
func (l *List) Init() *List {l.root.next = &l.rootl.root.prev = &l.rootl.len = 0return 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 = ate.next = at.nexte.prev.next = ee.next.prev = ee.list = ll.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.nexte.next.prev = e.preve.next = nil // avoid memory leakse.prev = nil // avoid memory leakse.list = nill.len--
}// move moves e to next to at.
func (l *List) move(e, at *Element) {if e == at {return}e.prev.next = e.nexte.next.prev = e.preve.prev = ate.next = at.nexte.prev.next = ee.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 crashl.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 lreturn 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 lreturn 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 ll.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 ll.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)}
}