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[pull] master from youngyangyang04:master #91

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pull merged 4 commits into AlgorithmAndLeetCode:master from youngyangyang04:master
Sep 18, 2022
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Create 707设计链表java代码的修改 
代码随想录网址上链表中的力扣707设计链表中的java代码:1,对于单链表的操作,删除元素的for循环跳出条件有误,进行了修改;2,对于双向链表,进行了插入头,尾元素和插入元素的统一操作。自己在原作者基础上写了一份设计链表的java代码。
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Tcotyledons authored Sep 13, 2022
commit ce5c5d010a778e9aadcacf903192b1da445206ff
187 changes: 187 additions & 0 deletions 707设计链表java代码的修改
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Original file line number Diff line number Diff line change
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//原来的代码随想录707设计链表的java代码中单链表的设计中有错误,修正后并对双链表进行了简化和更正,下面是我的java代码

//单链表
class ListNode{
int val;
ListNode next;
ListNode() {};
ListNode(int val){
this.val = val;
}
}


class MyLinkedList {

//记录链表中元素的数量
int size;
//记录链表的虚拟头结点
ListNode head;

public MyLinkedList() {
//初始化操作
this.size = 0;
this.head = new ListNode(0);
this.head.next = null;
}

public int get(int index) {
//判断index是否有效
if(index<0 || index>=size){
return -1;
}
ListNode cur = this.head;
//index 是可以取到的,因为有虚拟头结点
for(int i=0; i<= index; i++){
cur = cur.next;
}
return cur.val;
}

public void addAtHead(int val) {
//等价于在第0个元素前添加
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);
}

public void addAtIndex(int index, int val) {
//index大于链表长度
if(index>size){
return;
}
//index小于0
if(index<0){
index = 0;
}
size++;
//找到前驱
ListNode pre = this.head;
for(int i=0; i<index; i++){
pre = pre.next;
}
//新建结点
ListNode newNode = new ListNode(val);
newNode.next = pre.next;
pre.next = newNode;
}

public void deleteAtIndex(int index) {
//判断索引是否有效
if(index<0 || index>=size){
return;
}
//删除操作
size--;
ListNode pre = this.head;
for(int i=0; i<index; i++){
pre = pre.next;
}
pre.next = pre.next.next;

}
}

//-------------------------------------------------------------------------------------------------------------------------------
//双向链表
class ListNode{
int val;
ListNode next,prev;
ListNode() {};
ListNode(int val){
this.val = val;
}
}


class MyLinkedList {

//记录链表中元素的数量
int size;
//记录链表的虚拟头结点和尾结点
ListNode head,tail;

public MyLinkedList() {
//初始化操作
this.size = 0;
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;
tail.prev=head;
}

public int get(int index) {
//判断index是否有效
if(index<0 || index>=size){
return -1;
}
ListNode cur = this.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++){
cur = cur.prev;
}
}else{
for(int i=0; i<= index; i++){
cur = cur.next;
}
}
return cur.val;
}

public void addAtHead(int val) {
//等价于在第0个元素前添加
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);
}

public void addAtIndex(int index, int val) {
//index大于链表长度
if(index>size){
return;
}
//index小于0
if(index<0){
index = 0;
}
size++;
//找到前驱
ListNode pre = this.head;
for(int i=0; i<index; i++){
pre = pre.next;
}
//新建结点
ListNode newNode = new ListNode(val);
newNode.next = pre.next;
pre.next.prev = newNode;
newNode.prev = pre;
pre.next = newNode;

}

public void deleteAtIndex(int index) {
//判断索引是否有效
if(index<0 || index>=size){
return;
}
//删除操作
size--;
ListNode pre = this.head;
for(int i=0; i<index; i++){
pre = pre.next;
}
pre.next.next.prev = pre;
pre.next = pre.next.next;
}
}

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