509 lines
13 KiB
Markdown
509 lines
13 KiB
Markdown
---
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title: 链表
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description:
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published: true
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date: 2024-03-21T11:15:17.596Z
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tags: 算法
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editor: markdown
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dateCreated: 2024-03-21T11:15:17.596Z
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---
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# 移除链表元素
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题意：删除链表中等于给定值 val 的所有节点。
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示例 1： 输入：head = [1,2,6,3,4,5,6], val = 6 输出：[1,2,3,4,5]
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示例 2： 输入：head = [], val = 1 输出：[]
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示例 3： 输入：head = [7,7,7,7], val = 7 输出：[]
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```ts
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/**
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* Definition for singly-linked list.
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* class ListNode {
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* val: number
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* next: ListNode | null
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* constructor(val?: number, next?: ListNode | null) {
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* this.val = (val===undefined ? 0 : val)
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* this.next = (next===undefined ? null : next)
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* }
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* }
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*/
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function removeElements(head: ListNode | null, val: number): ListNode | null {
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let now = head;
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while (now?.next) {
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if (now.next.val === val) {
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now.next = now.next.next
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}else{
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now = now.next
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}
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}
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if (head?.val === val) {
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head = head?.next
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}
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return head;
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};
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```
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# 设计链表
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在链表类中实现这些功能：
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get(index)：获取链表中第 index 个节点的值。如果索引无效，则返回-1。
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addAtHead(val)：在链表的第一个元素之前添加一个值为 val 的节点。插入后，新节点将成为链表的第一个节点。
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addAtTail(val)：将值为 val 的节点追加到链表的最后一个元素。
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addAtIndex(index,val)：在链表中的第 index 个节点之前添加值为 val 的节点。如果 index 等于链表的长度，则该节点将附加到链表的末尾。如果 index 大于链表长度，则不会插入节点。如果index小于0，则在头部插入节点。
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deleteAtIndex(index)：如果索引 index 有效，则删除链表中的第 index 个节点。
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## 我的解法
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```ts
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// class ListNode {
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// public val: number;
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// public next: ListNode | null;
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// constructor(val?: number, next?: ListNode | null) {
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// this.val = val === undefined ? 0 : val;
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// this.next = next === undefined ? null : next;
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// }
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// }
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class MyLinkedList {
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private head: ListNode | null;
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constructor(head?: ListNode | null) {
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this.head = head !== undefined ? head : null;
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}
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get(index: number): number {
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let nowIndex = 0;
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let now = this.head;
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while (nowIndex++ < index) {
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if (now.next === null) return -1;
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now = now.next;
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}
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console.log('now', now)
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return now?.val !== undefined ? now?.val : -1;
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}
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addAtHead(val: number): void {
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let now = new ListNode();
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now.val = val;
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now.next = this.head;
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this.head = now;
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}
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addAtTail(val: number): void {
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let insertNode = new ListNode();
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let virHead = new ListNode();
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virHead.next = this.head;
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let now = virHead;
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while (now.next !== null) {
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now = now.next;
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}
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insertNode.val = val;
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now.next = insertNode;
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this.head = virHead.next;
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}
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addAtIndex(index: number, val: number): void {
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let nowIndex = -1;
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let insertNode = new ListNode();
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let virHead = new ListNode();
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virHead.next = this.head;
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let now = virHead;
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while (nowIndex++ < index - 1) {
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if (now.next === null) return;
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now = now.next;
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}
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insertNode.next = now?.next || null;
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insertNode.val = val;
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now.next = insertNode;
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this.head = virHead.next;
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}
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deleteAtIndex(index: number): void {
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let nowIndex = -1;
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let virHead = new ListNode();
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virHead.next = this.head;
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let now = virHead;
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while (nowIndex++ < index - 1) {
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if (now.next === null) return;
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now = now.next;
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}
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now.next = now.next?.next || null;
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this.head = virHead.next;
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}
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}
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```
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## 带size
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```ts
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class LinkedNode {
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public val: number;
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public next: LinkedNode;
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constructor(val: number) {
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this.val = val;
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this.next = null;
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}
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}
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class MyLinkedList {
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private size: number
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private head: LinkedNode;
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constructor() {
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this.size = 0;
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this.head = new LinkedNode(-1);
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}
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get(index: number): number {
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if (index < 0 || index >= this.size) {
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return -1;
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}
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let curr = this.head;
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let i = 0;
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while (i < index + 1) {
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curr = curr.next;
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i++;
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}
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return curr.val;
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}
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addAtHead(val: number): void {
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this.addAtIndex(0, val);
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}
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addAtTail(val: number): void {
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this.addAtIndex(this.size, val);
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}
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addAtIndex(index: number, val: number): void {
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if (index < 0 || index > this.size ) {
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return;
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}
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let curr = this.head;
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let i = 0;
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while (i < index) {
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curr = curr.next;
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i++;
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}
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const node = new LinkedNode(val);
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node.next = curr.next;
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curr.next = node;
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this.size++;
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}
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deleteAtIndex(index: number): void {
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if (index < 0 || index >= this.size) {
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return;
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}
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let curr = this.head;
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let i = 0;
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while (i < index) {
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curr = curr.next;
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i++;
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}
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curr.next = curr.next.next;
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this.size--;
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}
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}
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```
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## 带tail
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```ts
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// class ListNode {
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// public val: number;
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// public next: ListNode | null;
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// constructor(val?: number, next?: ListNode | null) {
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// this.val = val === undefined ? 0 : val;
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// this.next = next === undefined ? null : next;
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// }
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// }
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class MyLinkedList {
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// 记录链表长度
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private size: number;
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private head: ListNode | null;
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private tail: ListNode | null;
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constructor() {
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this.size = 0;
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this.head = null;
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this.tail = null;
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}
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// 获取链表中第 index个节点的值
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get(index: number): number {
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// 索引无效的情况
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if (index < 0 || index >= this.size) {
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return -1;
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}
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let curNode = this.getNode(index);
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// 这里在前置条件下，理论上不会出现 null的情况
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return curNode.val;
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}
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// 在链表的第一个元素之前添加一个值为 val的节点。插入后，新节点将成为链表的第一个节点。
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addAtHead(val: number): void {
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let node: ListNode = new ListNode(val, this.head);
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this.head = node;
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if (!this.tail) {
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this.tail = node;
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}
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this.size++;
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}
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// 将值为 val 的节点追加到链表的最后一个元素。
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addAtTail(val: number): void {
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let node: ListNode = new ListNode(val, null);
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if (this.tail) {
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this.tail.next = node;
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} else {
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// 还没有尾节点，说明一个节点都还没有
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this.head = node;
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}
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this.tail = node;
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this.size++;
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}
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// 在链表中的第 index个节点之前添加值为 val的节点。
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// 如果 index等于链表的长度，则该节点将附加到链表的末尾。如果 index大于链表长度，则不会插入节点。如果 index小于0，则在头部插入节点。
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addAtIndex(index: number, val: number): void {
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if (index === this.size) {
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this.addAtTail(val);
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return;
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}
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if (index > this.size) {
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return;
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}
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// <= 0 的情况都是在头部插入
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if (index <= 0) {
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this.addAtHead(val);
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return;
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}
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// 正常情况
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// 获取插入位置的前一个 node
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let curNode = this.getNode(index - 1);
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let node: ListNode = new ListNode(val, curNode.next);
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curNode.next = node;
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this.size++;
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}
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// 如果索引 index有效，则删除链表中的第 index个节点。
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deleteAtIndex(index: number): void {
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if (index < 0 || index >= this.size) {
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return;
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}
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// 处理头节点
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if (index === 0) {
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this.head = this.head!.next;
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// 如果链表中只有一个元素，删除头节点后，需要处理尾节点
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if (index === this.size - 1) {
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this.tail = null
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}
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this.size--;
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return;
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}
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// 索引有效
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let curNode: ListNode = this.getNode(index - 1);
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curNode.next = curNode.next!.next;
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// 处理尾节点
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if (index === this.size - 1) {
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this.tail = curNode;
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}
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this.size--;
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}
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// 获取指定 Node节点
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private getNode(index: number): ListNode {
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// 这里不存在没办法获取到节点的情况，都已经在前置方法做过判断
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// 创建虚拟头节点
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let curNode: ListNode = new ListNode(0, this.head);
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for (let i = 0; i <= index; i++) {
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// 理论上不会出现 null
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curNode = curNode.next!;
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}
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return curNode;
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}
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}
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```
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# 翻转链表
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## 双指针
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```ts
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/**
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* Definition for singly-linked list.
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* class ListNode {
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* val: number
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* next: ListNode | null
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* constructor(val?: number, next?: ListNode | null) {
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* this.val = (val===undefined ? 0 : val)
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* this.next = (next===undefined ? null : next)
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* }
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* }
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*/
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function reverseList(head: ListNode | null): ListNode | null {
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let preNode: ListNode | null = null,
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curNode: ListNode | null = head,
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tempNode: ListNode | null;
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while (curNode) {
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tempNode = curNode.next;
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curNode.next = preNode;
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preNode = curNode;
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curNode = tempNode;
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}
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return preNode;
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};
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```
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## 递归
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```ts
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/**
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* Definition for singly-linked list.
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* class ListNode {
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* val: number
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* next: ListNode | null
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* constructor(val?: number, next?: ListNode | null) {
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* this.val = (val===undefined ? 0 : val)
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* this.next = (next===undefined ? null : next)
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* }
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* }
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*/
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function reverseList(head: ListNode | null): ListNode | null {
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function reserve(tail, head) {
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if (head === null) {
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return tail;
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}
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let tmp = head.next;
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head.next = tail;
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tail = head;
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return reserve(tail, tmp)
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}
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return reserve(null, head)
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};
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```
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# 两两交换链表中的节点
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示例 1：
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输入：head = [1,2,3,4]
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输出：[2,1,4,3]
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示例 2：
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输入：head = []
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输出：[]
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示例 3：
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输入：head = [1]
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输出：[1]
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```ts
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/**
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* Definition for singly-linked list.
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* class ListNode {
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* val: number
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* next: ListNode | null
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* constructor(val?: number, next?: ListNode | null) {
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* this.val = (val===undefined ? 0 : val)
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* this.next = (next===undefined ? null : next)
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* }
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* }
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*/
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function swapPairs(head: ListNode | null): ListNode | null {
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let virHead = new ListNode();
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virHead.next = head;
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let cur = virHead;
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while (cur.next && cur.next.next) {
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let temp = cur.next;
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let temp2Next = cur.next.next.next;
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cur.next = temp.next;
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temp.next.next = temp;
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temp.next = temp2Next;
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cur = cur.next.next
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}
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return virHead.next
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};
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```
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# 删除链表的倒数第N个节点
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输入：head = [1,2,3,4,5], n = 2 输出：[1,2,3,5] 示例 2：
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输入：head = [1], n = 1 输出：[] 示例 3：
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输入：head = [1,2], n = 1 输出：[1]
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```ts
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function removeNthFromEnd(head: ListNode | null, n: number): ListNode | null {
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let times = 0;
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const virHead = new ListNode();
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virHead.next = head;
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let tail = virHead;
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let del = virHead;
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while (times < n && tail?.next) {
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tail = tail.next;
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times++
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}
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if (times < n) return head;
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while (tail.next) {
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del = del.next;
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tail = tail.next;
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}
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del.next = del.next.next
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return virHead.next;
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};
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```
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# 链表相交
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```js
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var getIntersectionNode = function (headA, headB) {
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let curA = headA;
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let curB = headB;
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let sizeA = 0, sizeB = 0;
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while (curA?.next) {
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curA = curA.next;
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sizeA++
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}
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while (curB?.next) {
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curB = curB.next;
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sizeB++
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}
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const diffNum = Math.abs(sizeA - sizeB);
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curA = headA;
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curB = headB;
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if (sizeA >= sizeB) {
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for (let n = 0; n < diffNum; n++) {
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curA = curA.next;
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}
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} else {
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for (let n = 0; n < diffNum; n++) {
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curB = curB.next;
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}
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}
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while (curA !== curB) {
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curA = curA?.next;
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curB = curB?.next;
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}
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return curA;
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};
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```
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# 环形链表II
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```ts
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function detectCycle(head: ListNode | null): ListNode | null {
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let fast = head, slow = head;
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while (fast !== null && fast.next !== null) {
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fast = fast.next.next;
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slow = slow.next;
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if (fast === slow) {
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let index1 = head;
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let index2 = fast;
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while (index1 !== index2) {
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index1 = index1.next;
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index2 = index2.next;
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}
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return index2
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}
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}
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return null;
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};
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```
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