Merge pull request #2132 from RS-maker975/master

对0707设计链表，go版本单链表做了修改，原来版本没有删除链表指定index下标的方法，并且已有的在leetcode执行有误，做了修改调…

problems/0707.设计链表.md

@@ -663,100 +663,128 @@ Go：
 //单链表实现
 package main
 
-import "fmt"
-
-func main() {
-	var list = new(SingleLinkedList)
-	list.Init()
-	list.addAtHead(100)
-	list.addAtTail(242)
-	list.addAtTail(777)
-	list.addAtIndex(1, 99999)
-	list.printLinkedList()
-}
-
-// 单链表写法 //
+import (
+	"fmt"
+)
 
 type SingleNode struct {
-	Val  int
-	Next *SingleNode
+	Val  int         // 节点的值
+	Next *SingleNode // 下一个节点的指针
 }
 
-type SingleLinkedList struct {
-	dummyHead *SingleNode
-	Size      int
+type MyLinkedList struct {
+	dummyHead *SingleNode // 虚拟头节点
+	Size      int         // 链表大小
 }
 
-// 初始化链表
-func (list *SingleLinkedList) Init() *SingleLinkedList {
-	list.Size = 0
-	list.dummyHead = new(SingleNode)
-	return list
+func main() {
+	list := Constructor()     // 初始化链表
+	list.AddAtHead(100)       // 在头部添加元素
+	list.AddAtTail(242)       // 在尾部添加元素
+	list.AddAtTail(777)       // 在尾部添加元素
+	list.AddAtIndex(1, 99999) // 在指定位置添加元素
+	list.printLinkedList()    // 打印链表
 }
 
-// 获取第index个节点数值
-func (list *SingleLinkedList) get(index int) int {
-	if list != nil || index < 0 || index > list.Size {
+/** Initialize your data structure here. */
+func Constructor() MyLinkedList {
+	newNode := &SingleNode{ // 创建新节点
+		-999,
+		nil,
+	}
+	return MyLinkedList{ // 返回链表
+		dummyHead: newNode,
+		Size:      0,
+	}
+
+}
+
+/** 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 {
+	/*if this != nil || index < 0 || index > this.Size {
+		return -1
+	}*/
+	if this == nil || index < 0 || index >= this.Size { // 如果索引无效则返回-1
 		return -1
 	}
 	// 让cur等于真正头节点
-	cur := list.dummyHead.Next
-	for i := 0; i < index; i++ {
+	cur := this.dummyHead.Next   // 设置当前节点为真实头节点
+	for i := 0; i < index; i++ { // 遍历到索引所在的节点
 		cur = cur.Next
 	}
-	return cur.Val
+	return cur.Val // 返回节点值
 }
 
-// 在链表最前面插入一个节点
-func (list *SingleLinkedList) addAtHead(val int) {
+/** 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) {
 	// 以下两行代码可用一行代替
 	// newNode := new(SingleNode)
 	// newNode.Val = val
-	newNode := &SingleNode{Val: val}
-
-	newNode.Next = list.dummyHead.Next
-	list.dummyHead.Next = newNode
-	list.Size++
+	newNode := &SingleNode{Val: val}   // 创建新节点
+	newNode.Next = this.dummyHead.Next // 新节点指向当前头节点
+	this.dummyHead.Next = newNode      // 新节点变为头节点
+	this.Size++                        // 链表大小增加1
 }
 
-// 在链表最后面插入一个节点
-func (list *SingleLinkedList) addAtTail(val int) {
-	newNode := &SingleNode{Val: val}
-	cur := list.dummyHead
-	for cur.Next != nil {
+/** Append a node of value val to the last element of the linked list. */
+func (this *MyLinkedList) AddAtTail(val int) {
+	newNode := &SingleNode{Val: val} // 创建新节点
+	cur := this.dummyHead            // 设置当前节点为虚拟头节点
+	for cur.Next != nil {            // 遍历到最后一个节点
 		cur = cur.Next
 	}
-	cur.Next = newNode
-	list.Size++
+	cur.Next = newNode // 在尾部添加新节点
+	this.Size++        // 链表大小增加1
 }
 
-// 打印链表
-func (list *SingleLinkedList) printLinkedList() {
-	cur := list.dummyHead
-	for cur.Next != nil {
-		fmt.Println(cur.Next.Val)
-		cur = cur.Next
-	}
-}
-
-// 在第index个节点之前插入新节点
-func (list *SingleLinkedList) addAtIndex(index int, val int) {
-	if index < 0 {
+/** 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) {
+	if index < 0 { // 如果索引小于0，设置为0
 		index = 0
-	} else if index > list.Size {
+	} else if index > this.Size { // 如果索引大于链表长度，直接返回
 		return
 	}
 
-	newNode := &SingleNode{Val: val}
-	cur := list.dummyHead //用虚拟头节点不用考虑在头部插入的情况
-	for i := 0; i < index; i++ {
+	newNode := &SingleNode{Val: val} // 创建新节点
+	cur := this.dummyHead            // 设置当前节点为虚拟头节点
+	for i := 0; i < index; i++ {     // 遍历到指定索引的前一个节点
 		cur = cur.Next
 	}
-	newNode.Next = cur.Next
-	cur.Next = newNode
-	list.Size++
+	newNode.Next = cur.Next // 新节点指向原索引节点
+	cur.Next = newNode      // 原索引的前一个节点指向新节点
+	this.Size++             // 链表大小增加1
 }
 
+/** Delete the index-th node in the linked list, if the index is valid. */
+func (this *MyLinkedList) DeleteAtIndex(index int) {
+	if index < 0 || index >= this.Size { // 如果索引无效则直接返回
+		return
+	}
+	cur := this.dummyHead        // 设置当前节点为虚拟头节点
+	for i := 0; i < index; i++ { // 遍历到要删除节点的前一个节点
+		cur = cur.Next
+	}
+	if cur.Next != nil {
+		cur.Next = cur.Next.Next // 当前节点直接指向下下个节点，即删除了下一个节点
+	}
+	this.Size-- // 注意删除节点后应将链表大小减一
+}
+
+// 打印链表
+func (list *MyLinkedList) printLinkedList() {
+	cur := list.dummyHead // 设置当前节点为虚拟头节点
+	for cur.Next != nil { // 遍历链表
+		fmt.Println(cur.Next.Val) // 打印节点值
+		cur = cur.Next            // 切换到下一个节点
+	}
+}
+
+
 ```
 
 ```go