From bf6e250c4afba01927056b30407bf43ce1cf010a Mon Sep 17 00:00:00 2001
From: resyon <hirosakae7@gmail.com>
Date: Sun, 23 May 2021 12:44:45 +0800
Subject: [PATCH] add 0707-golang

---
 problems/0707.设计链表.md | 121 ++++++++++++++++++++++++++++++++++
 1 file changed, 121 insertions(+)

diff --git a/problems/0707.设计链表.md b/problems/0707.设计链表.md
index a4f4d8d3..1ca72e54 100644
--- a/problems/0707.设计链表.md
+++ b/problems/0707.设计链表.md
@@ -393,6 +393,127 @@ class MyLinkedList:
 
 Go：
 
+```go
+//循环双链表
+type MyLinkedList struct {
+	dummy *Node
+}
+
+type Node struct {
+	Val  int
+	Next *Node
+	Pre  *Node
+}
+
+//仅保存哑节点，pre-> rear, next-> head
+/** Initialize your data structure here. */
+func Constructor() MyLinkedList {
+	rear := &Node{
+		Val:  -1,
+		Next: nil,
+		Pre:  nil,
+	}
+	rear.Next = rear
+	rear.Pre = rear
+	return MyLinkedList{rear}
+}
+
+/** Get the value of the index-th node in the linked list. If the index is invalid, return -1. */
+func (this *MyLinkedList) Get(index int) int {
+	head := this.dummy.Next
+	//head == this, 遍历完全
+	for head != this.dummy && index > 0 {
+		index--
+		head = head.Next
+	}
+	//否则, head == this, 索引无效
+	if 0 != index {
+		return -1
+	}
+	return head.Val
+}
+
+/** Add a node of value val before the first element of the linked list. After the insertion, the new node will be the first node of the linked list. */
+func (this *MyLinkedList) AddAtHead(val int) {
+	dummy := this.dummy
+	node := &Node{
+		Val: val,
+		//head.Next指向原头节点
+		Next: dummy.Next,
+		//head.Pre 指向哑节点
+		Pre: dummy,
+	}
+
+	//更新原头节点
+	dummy.Next.Pre = node
+	//更新哑节点
+	dummy.Next = node
+	//以上两步不能反
+}
+
+/** Append a node of value val to the last element of the linked list. */
+func (this *MyLinkedList) AddAtTail(val int) {
+	dummy := this.dummy
+	rear := &Node{
+		Val: val,
+		//rear.Next = dummy(哑节点)
+		Next: dummy,
+		//rear.Pre = ori_rear
+		Pre: dummy.Pre,
+	}
+
+	//ori_rear.Next = rear
+	dummy.Pre.Next = rear
+	//update dummy
+	dummy.Pre = rear
+	//以上两步不能反
+}
+
+/** Add a node of value val before the index-th node in the linked list. If index equals to the length of linked list, the node will be appended to the end of linked list. If index is greater than the length, the node will not be inserted. */
+func (this *MyLinkedList) AddAtIndex(index int, val int) {
+	head := this.dummy.Next
+	//head = MyLinkedList[index]
+	for head != this.dummy && index > 0 {
+		head = head.Next
+		index--
+	}
+	node := &Node{
+		Val: val,
+		//node.Next = MyLinkedList[index]
+		Next: head,
+		//node.Pre = MyLinkedList[index-1]
+		Pre: head.Pre,
+	}
+	//MyLinkedList[index-1].Next = node
+	head.Pre.Next = node
+	//MyLinkedList[index].Pre = node
+	head.Pre = node
+	//以上两步不能反
+}
+
+/** Delete the index-th node in the linked list, if the index is valid. */
+func (this *MyLinkedList) DeleteAtIndex(index int) {
+	//链表为空
+	if this.dummy.Next == this.dummy {
+		return
+	}
+	head := this.dummy.Next
+	//head = MyLinkedList[index]
+	for head.Next != this.dummy && index > 0 {
+		head = head.Next
+		index--
+	}
+	//验证index有效
+	if index == 0 {
+		//MyLinkedList[index].Pre = index[index-2]
+		head.Next.Pre = head.Pre
+		//MyLinedList[index-2].Next = index[index]
+		head.Pre.Next = head.Next
+		//以上两步顺序无所谓
+	}
+}
+```
+
 javaScript:
 
 ```js