modified 707 code, move the ListNode class inside, reformat the code

problems/0707.设计链表.md

@@ -422,38 +422,38 @@ void myLinkedListFree(MyLinkedList* obj) {
 
 ```Java
 //单链表
-class ListNode {
-    int val;
-    ListNode next;
-    ListNode(){}
-    ListNode(int val) {
-        this.val=val;
-    }
-}
 class MyLinkedList {
+
+    class ListNode {
+        int val;
+        ListNode next;
+        ListNode(int val) {
+            this.val=val;
+        }
+    }
     //size存储链表元素的个数
-    int size;
+    private int size;
-    //虚拟头结点
+    //注意这里记录的是虚拟头结点
-    ListNode head;
+    private ListNode head;
 
     //初始化链表
     public MyLinkedList() {
-        size = 0;
+        this.size = 0;
-        head = new ListNode(0);
+        this.head = new ListNode(0);
     }
 
-    //获取第index个节点的数值，注意index是从0开始的，第0个节点就是头结点
+    //获取第index个节点的数值，注意index是从0开始的，第0个节点就是虚拟头结点
     public int get(int index) {
         //如果index非法，返回-1
         if (index < 0 || index >= size) {
             return -1;
         }
-        ListNode currentNode = head;
+        ListNode cur = head;
-        //包含一个虚拟头节点，所以查找第 index+1 个节点
+        //第0个节点是虚拟头节点，所以查找第 index+1 个节点
         for (int i = 0; i <= index; i++) {
-            currentNode = currentNode.next;
+            cur = cur.next;
         }
-        return currentNode.val;
+        return cur.val;
     }
 
     public void addAtHead(int val) {
@@ -473,7 +473,6 @@ class MyLinkedList {
         while (cur.next != null) {
             cur = cur.next;
         }
-
         cur.next = newNode;
         size++;
 
@@ -485,55 +484,53 @@ class MyLinkedList {
     // 如果 index 等于链表的长度，则说明是新插入的节点为链表的尾结点
     // 如果 index 大于链表的长度，则返回空
     public void addAtIndex(int index, int val) {
-        if (index > size) {
+        if (index < 0 || index > size) {
             return;
         }
-        if (index < 0) {
+
-            index = 0;
-        }
-        size++;
         //找到要插入节点的前驱
-        ListNode pred = head;
+        ListNode pre = head;
         for (int i = 0; i < index; i++) {
-            pred = pred.next;
+            pre = pre.next;
         }
-        ListNode toAdd = new ListNode(val);
+        ListNode newNode = new ListNode(val);
-        toAdd.next = pred.next;
+        newNode.next = pre.next;
-        pred.next = toAdd;
+        pre.next = newNode;
+        size++;
     }
 
-    //删除第index个节点
     public void deleteAtIndex(int index) {
         if (index < 0 || index >= size) {
             return;
         }
-        size--;
+        
-        //因为有虚拟头节点，所以不用对Index=0的情况进行特殊处理
+        //因为有虚拟头节点，所以不用对index=0的情况进行特殊处理
-        ListNode pred = head;
+        ListNode pre = head;
         for (int i = 0; i < index ; i++) {
-            pred = pred.next;
+            pre = pre.next;
         }
-        pred.next = pred.next.next;
+        pre.next = pre.next.next;
+        size--;
     }
 }
+```
 
+```Java
 //双链表
-class ListNode{
-    int val;
-    ListNode next,prev;
-    ListNode() {};
-    ListNode(int val){
-        this.val = val;
-    }
-}
-
-
 class MyLinkedList {  
 
+    class ListNode{
+        int val;
+        ListNode next, prev;
+        ListNode(int val){
+            this.val = val;
+        }
+    }
+
     //记录链表中元素的数量
-    int size;
+    private int size;
     //记录链表的虚拟头结点和尾结点
-    ListNode head,tail;
+    private ListNode head, tail;
     
     public MyLinkedList() {
         //初始化操作
@@ -541,25 +538,25 @@ class MyLinkedList {
         this.head = new ListNode(0);
         this.tail = new ListNode(0);
         //这一步非常关键，否则在加入头结点的操作中会出现null.next的错误！！！
-        head.next=tail;
+        this.head.next = tail;
-        tail.prev=head;
+        this.tail.prev = head;
     }
     
     public int get(int index) {
         //判断index是否有效
-        if(index>=size){
+        if(index < 0 || index >= size){
             return -1;
         }
-        ListNode cur = this.head;
+        ListNode cur = head;
         //判断是哪一边遍历时间更短
         if(index >= size / 2){
             //tail开始
             cur = tail;
-            for(int i=0; i< size-index; i++){
+            for(int i = 0; i < size - index; i++){
                 cur = cur.prev;
             }
         }else{
-            for(int i=0; i<= index; i++){
+            for(int i = 0; i <= index; i++){
                 cur = cur.next; 
             }
         }
@@ -568,24 +565,23 @@ class MyLinkedList {
     
     public void addAtHead(int val) {
         //等价于在第0个元素前添加
-        addAtIndex(0,val);
+        addAtIndex(0, val);
     }
     
     public void addAtTail(int val) {
         //等价于在最后一个元素(null)前添加
-        addAtIndex(size,val);
+        addAtIndex(size, val);
     }
     
     public void addAtIndex(int index, int val) {
-        //index大于链表长度
+        //判断index是否有效
-        if(index>size){
+        if(index < 0 || index > size){
             return;
         }
 
-        size++;
         //找到前驱
-        ListNode pre = this.head;
+        ListNode pre = head;
-        for(int i=0; i<index; i++){
+        for(int i = 0; i < index; i++){
             pre = pre.next;
         }
         //新建结点
@@ -594,22 +590,24 @@ class MyLinkedList {
         pre.next.prev = newNode;
         newNode.prev = pre;
         pre.next = newNode;
+        size++;
         
     }
     
     public void deleteAtIndex(int index) {
-        //判断索引是否有效
+        //判断index是否有效
-        if(index>=size){
+        if(index < 0 || index >= size){
             return;
         }
+
         //删除操作
-        size--;
+        ListNode pre = head;
-        ListNode pre = this.head;
+        for(int i = 0; i < index; i++){
-        for(int i=0; i<index; i++){
             pre = pre.next;
         }
         pre.next.next.prev = pre;
         pre.next = pre.next.next;
+        size--;
     }
 }