数据结构--链表（单向链表）
一.链表的概念
链表是一种物理存储结构上非连续存储结构，数据元素的逻辑顺序是通过链表中的引用链接次序实现的 ，有单向链表和双向链表。
二.单向结构
三.单向链表的模拟实现
public class Mylink {
private ListNode head;
class ListNode{
public int value ;
public ListNode next;
public ListNode(int value) {
this.value = value;
}
}
//得到单链表的长度
public int size(){
ListNode cur =head;
int count=0;
while (cur!=null){
cur=cur.next;
count++;
}
return count;
}
//遍历
public void display() {
ListNode cur =head;
while (cur!=null){
System.out.print(cur.value+" ");
cur=cur.next;
}
System.out.println();
}
//查找是否包含关键字key是否在单链表当中
public boolean contains(int key){
ListNode cur =head;
while (cur!=null){
if (cur.value==key){
return true;
}
cur=cur.next;
}
return false;
}
//头插法
public void addFirst(int data){
ListNode newnode =new ListNode(data);
newnode.next=head;
head=newnode;
}
//尾插法
public void addLast(int data){
ListNode cur =head;
ListNode newnode=new ListNode(data);
if (head==null){
head=newnode;
return;
}
while (cur.next!=null){
cur=cur.next;
}
cur.next=newnode;
}
public void checkPos(int index)throws PostExpect{
if (index<0||index>size()){
throw new PostExpect("下标异常");
}
}
//任意位置插入,第一个数据节点为0号下标
public void addIndex(int index,int data){
try {
checkPos(index);
ListNode cur =head;
ListNode newnode =new ListNode(data);
if (index==0){
addFirst(data);
}
if (index==size()){
addLast(data);
}else {
for (int i = index-1; i > 0; i--) {
cur=cur.next;
}
newnode.next=cur.next;
cur.next=newnode;
}
}catch (PostExpect e){
e.printStackTrace();
}
}
//删除第一次出现关键字为key的节点
public void remove(int key){
if (head==null){
return;
}
ListNode cur =head;
if (cur.value==key){
head =cur.next;
return;
}
while (cur.next!=null){
if (cur.next.value==key){
ListNode del =cur.next;
cur.next=del.next;
return;
}
cur=cur.next;
}
}
//删除所有值为key的节点
public void removeAllKey(int key){
if (head==null){
return;
}
ListNode cur =head.next;
ListNode pre =head;
while (cur!=null){
if (cur.value==key){
pre.next=cur.next;
cur=cur.next;
}else {
cur=cur.next;
pre=pre.next;
}
}
if (head.value==key){
head=head.next;
}
}
//清空链表
public void clear() {
head=null;
}
}1.注意事项：
2.额外的方法
2.1 反转链表
代码：
public ListNode reverseList() {
if(head==null){
return null;
}
ListNode cur =head.next;
head.next =null;
while(cur!=null){
ListNode curt =cur.next;
cur.next=head;
head=cur;
cur=curt;
}
return head;
}举例：
2.2 返回中间节点
代码：
//方法一
public ListNode middleNode() {
if(head==null){
return null;
}
ListNode cur =head;
int count =0;
while(cur!=null){
count++;
cur=cur.next;
}
count=count/2;
while(count>0){
count--;
head=head.next;
}
return head;
}
//方法二：
public ListNode middleNode2() {
if(head==null){
return null;
}
ListNode cur =head;
ListNode slow =head;
ListNode fast =head;
while(fast!=null&&fast.next!=null){
fast=fast.next.next;
slow=slow.next;
}
return slow;
}2.3 放回倒数第K个节点的值
代码：
//k值有效
//方法1：
public int kthToLast(int k) {
if(head==null){
return -1;
}
ListNode cur =head;
int count =0;
while(cur!=null){
count++;
cur=cur.next;
}
int num =count-k;
while(num>0){
num--;
head=head.next;
}
return head.value;
}
//方法2：
public int kthToLast1( int k) {
if(head==null){
return -1;
}
ListNode fast =head;
ListNode slow =head;
while(k-->0){
fast =fast.next; //使slow和fast差 k 步
}
while(fast!=null){ //当fast为空时slow与fast差 k 个节点，slow为倒数第 k 个节点
fast=fast.next;
slow=slow.next;
}
return slow.value;
}2.4合并俩个有序链表
代码：
public ListNode mergeTwoLists(ListNode headA, ListNode headB) {
if(headA==null&&headB==null){
return null;
}
ListNode head =new ListNode();
ListNode cur =head;
while(headA!=null&&headB!=null){
if(headA.val>headB.val){
cur.next=headB;
headB=headB.next;
cur=cur.next;
}else{
cur.next=headA;
headA=headA.next;
cur=cur.next;
}
}
if(headA==null){
cur.next=headB;
}
if(headB==null){
cur.next=headA;
}
return head.next;
}2.5 将小于X的节点排在X之前
代码：
public ListNode partition(int x) {
if(head==null){
return null;
}
ListNode cur =head;
ListNode as =null;
ListNode bs =null;
ListNode be =null;
ListNode ae =null;
while(cur!=null){
if(cur.value2.6判断是否回文
代码：
public boolean chkPalindrome(ListNode head) {
ListNode cur =head;
ListNode slow =head;
ListNode fast =head;
ListNode last =head;
while(fast!=null&&fast.next!=null){
fast=fast.next.next;
slow=slow.next;
}
last=slow.next;
while(last!=null){
ListNode tmp =last.next;
last.next=slow;
slow=last;
last=tmp;
}
while(head!=slow){
if(head.val==slow.val){
if(head.next==slow){
return true;
}
slow=slow.next;
head=head.next;
}else{
return false;
}
}
return true;2.7找俩条链表相交得节点
代码：
public ListNode getIntersectionNode(ListNode listA, ListNode listB) {
if(listA==null||listB==null){
return null;
}
ListNode as =listA;
ListNode bs =listB;
int numA=0;
int numB=0;
while(as!=null){
as=as.next;
numA++;
}
while(bs!=null){
bs=bs.next;
numB++;
}
if(numA>numB){
int k=numA-numB;
while(k>0){
listA=listA.next;
k--;
}
}else{
int k=numB-numA;
while(k>0){
listB=listB.next;
k--;
}
}
while(listA!=listB){
listA=listA.next;
listB=listB.next;
}
if(listA==null){
return null;
}
return listA;
}2.8 判断是否有环
代码：
public boolean hasCycle(ListNode head) {
if(head==null){
return false;
}
ListNode fast =head;
ListNode slow=head;
while(fast!=null&&fast.next!=null){
fast=fast.next.next;
slow=slow.next;
if(fast==slow){
return true;
}
}
return false;2.9找刚进入环点的节点
public ListNode detectCycle(ListNode head) {
if(head==null){
return null;
}
ListNode fast =head;
ListNode slow=head;
while(fast!=null&&fast.next!=null){
fast=fast.next.next;
slow=slow.next;
if(fast==slow){
break;
}
}
if(fast==null||fast.next==null){
return null;
}
while(fast!=head){
head=head.next;
fast=fast.next;
}
return head;
}