docs: create 算法/链表

算法/链表.md

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+---
+title: 链表
+description: 
+published: true
+date: 2024-03-21T11:15:17.596Z
+tags: 算法
+editor: markdown
+dateCreated: 2024-03-21T11:15:17.596Z
+---
+
+# 移除链表元素
+题意：删除链表中等于给定值 val 的所有节点。
+
+示例 1： 输入：head = [1,2,6,3,4,5,6], val = 6 输出：[1,2,3,4,5]
+
+示例 2： 输入：head = [], val = 1 输出：[]
+
+示例 3： 输入：head = [7,7,7,7], val = 7 输出：[]
+```ts
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     val: number
+ *     next: ListNode | null
+ *     constructor(val?: number, next?: ListNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.next = (next===undefined ? null : next)
+ *     }
+ * }
+ */
+
+function removeElements(head: ListNode | null, val: number): ListNode | null {
+    let now = head;
+    while (now?.next) {
+        if (now.next.val === val) {
+            now.next = now.next.next
+        }else{
+            now = now.next
+        }
+    }
+    if (head?.val === val) {
+        head = head?.next
+    }
+    return head;
+};
+```
+
+# 设计链表
+在链表类中实现这些功能：
+
+get(index)：获取链表中第 index 个节点的值。如果索引无效，则返回-1。
+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。
+addAtTail(val)：将值为 val 的节点追加到链表的最后一个元素。
+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。
+deleteAtIndex(index)：如果索引 index 有效，则删除链表中的第 index 个节点。
+
+## 我的解法
+```ts
+// class ListNode {
+//     public val: number;
+//     public next: ListNode | null;
+//     constructor(val?: number, next?: ListNode | null) {
+//         this.val = val === undefined ? 0 : val;
+//         this.next = next === undefined ? null : next;
+//     }
+// }
+
+class MyLinkedList {
+    private head: ListNode | null;
+    constructor(head?: ListNode | null) {
+        this.head = head !== undefined ? head : null;
+    }
+
+    get(index: number): number {
+        let nowIndex = 0;
+        let now = this.head;
+        while (nowIndex++ < index) {
+            if (now.next === null) return -1;
+            now = now.next;
+        }
+        console.log('now', now)
+        return now?.val !== undefined ? now?.val : -1;
+    }
+
+    addAtHead(val: number): void {
+        let now = new ListNode();
+        now.val = val;
+        now.next = this.head;
+        this.head = now;
+    }
+
+    addAtTail(val: number): void {
+        let insertNode = new ListNode();
+        let virHead = new ListNode();
+        virHead.next = this.head;
+        let now = virHead;
+        while (now.next !== null) {
+            now = now.next;
+        }
+        insertNode.val = val;
+        now.next = insertNode;
+        this.head = virHead.next;
+    }
+
+    addAtIndex(index: number, val: number): void {
+        let nowIndex = -1;
+        let insertNode = new ListNode();
+        let virHead = new ListNode();
+        virHead.next = this.head;
+        let now = virHead;
+        while (nowIndex++ < index - 1) {
+            if (now.next === null) return;
+            now = now.next;
+        }
+        insertNode.next = now?.next || null;
+        insertNode.val = val;
+        now.next = insertNode;
+        this.head = virHead.next;
+    }
+
+    deleteAtIndex(index: number): void {
+        let nowIndex = -1;
+        let virHead = new ListNode();
+        virHead.next = this.head;
+        let now = virHead;
+        while (nowIndex++ < index - 1) {
+            if (now.next === null) return;
+            now = now.next;
+        }
+        now.next = now.next?.next || null;
+        this.head = virHead.next;
+    }
+}
+```
+
+## 带size
+```ts
+class LinkedNode {
+    public val: number;
+    public next: LinkedNode;
+
+    constructor(val: number) {
+        this.val = val;
+        this.next = null;
+    }
+}
+
+class MyLinkedList {
+    private size: number
+    private head: LinkedNode;
+    constructor() {
+        this.size = 0;
+        this.head = new LinkedNode(-1);
+    }
+
+    get(index: number): number {
+        if (index < 0 || index >= this.size) {
+            return -1;
+        } 
+
+        let curr = this.head;
+        let i = 0;
+        while (i < index + 1) {
+            curr = curr.next;
+            i++;
+        }
+
+        return curr.val;
+    }
+
+    addAtHead(val: number): void {
+        this.addAtIndex(0, val);
+    }
+
+    addAtTail(val: number): void {
+        this.addAtIndex(this.size, val);
+    }
+
+    addAtIndex(index: number, val: number): void {
+        if (index < 0 || index > this.size ) {
+            return;
+        }
+        
+        let curr = this.head;
+        let i = 0;
+        while (i < index) {
+            curr = curr.next;
+            i++;
+        }
+
+        const node = new LinkedNode(val);
+        node.next = curr.next;
+        curr.next = node;
+
+        this.size++;
+    }
+
+    deleteAtIndex(index: number): void {
+        if (index < 0 || index >= this.size) {
+            return;
+        }
+
+        let curr = this.head;
+        let i = 0;
+        while (i < index) {
+            curr = curr.next;
+            i++;
+        }
+
+        curr.next = curr.next.next;
+
+        this.size--;
+    }
+}
+```
+## 带tail
+```ts
+// class ListNode {
+//     public val: number;
+//     public next: ListNode | null;
+//     constructor(val?: number, next?: ListNode | null) {
+//         this.val = val === undefined ? 0 : val;
+//         this.next = next === undefined ? null : next;
+//     }
+// }
+
+class MyLinkedList {
+    // 记录链表长度
+    private size: number;
+    private head: ListNode | null;
+    private tail: ListNode | null;
+    constructor() {
+        this.size = 0;
+        this.head = null;
+        this.tail = null;
+    }
+
+    // 获取链表中第 index个节点的值
+    get(index: number): number {
+        // 索引无效的情况
+        if (index < 0 || index >= this.size) {
+            return -1;
+        }
+        let curNode = this.getNode(index);
+        // 这里在前置条件下，理论上不会出现 null的情况
+        return curNode.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。
+    addAtHead(val: number): void {
+        let node: ListNode = new ListNode(val, this.head);
+        this.head = node;
+        if (!this.tail) {
+            this.tail = node;
+        }
+        this.size++;
+    }
+
+    // 将值为 val 的节点追加到链表的最后一个元素。
+    addAtTail(val: number): void {
+        let node: ListNode = new ListNode(val, null);
+        if (this.tail) {
+            this.tail.next = node;
+        } else {
+            // 还没有尾节点，说明一个节点都还没有
+            this.head = node;
+        }
+        this.tail = node;
+        this.size++;
+    }
+
+    // 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。
+    addAtIndex(index: number, val: number): void {
+        if (index === this.size) {
+            this.addAtTail(val);
+            return;
+        }
+        if (index > this.size) {
+            return;
+        }
+        // <= 0 的情况都是在头部插入
+        if (index <= 0) {
+            this.addAtHead(val);
+            return;
+        }
+        // 正常情况
+        // 获取插入位置的前一个 node
+        let curNode = this.getNode(index - 1);
+        let node: ListNode = new ListNode(val, curNode.next);
+        curNode.next = node;
+        this.size++;
+    }
+
+    // 如果索引 index有效，则删除链表中的第 index个节点。
+    deleteAtIndex(index: number): void {
+        if (index < 0 || index >= this.size) {
+            return;
+        }
+        // 处理头节点
+        if (index === 0) {
+            this.head = this.head!.next;
+            // 如果链表中只有一个元素，删除头节点后，需要处理尾节点
+            if (index === this.size - 1) {
+                this.tail = null
+            }
+            this.size--;
+            return;
+        }
+        // 索引有效
+        let curNode: ListNode = this.getNode(index - 1);
+        curNode.next = curNode.next!.next;
+        // 处理尾节点
+        if (index === this.size - 1) {
+            this.tail = curNode;
+        }
+        this.size--;
+    }
+
+    // 获取指定 Node节点
+    private getNode(index: number): ListNode {
+        // 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
+        // 创建虚拟头节点
+        let curNode: ListNode = new ListNode(0, this.head);
+        for (let i = 0; i <= index; i++) {
+            // 理论上不会出现 null
+            curNode = curNode.next!;
+        }
+        return curNode;
+    }
+}
+```
+# 翻转链表
+## 双指针
+```ts
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     val: number
+ *     next: ListNode | null
+ *     constructor(val?: number, next?: ListNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.next = (next===undefined ? null : next)
+ *     }
+ * }
+ */
+
+function reverseList(head: ListNode | null): ListNode | null {
+    let preNode: ListNode | null = null,
+        curNode: ListNode | null = head,
+        tempNode: ListNode | null;
+    while (curNode) {
+        tempNode = curNode.next;
+        curNode.next = preNode;
+        preNode = curNode;
+        curNode = tempNode;
+    }
+    return preNode;
+};
+```
+## 递归
+```ts
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     val: number
+ *     next: ListNode | null
+ *     constructor(val?: number, next?: ListNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.next = (next===undefined ? null : next)
+ *     }
+ * }
+ */
+function reverseList(head: ListNode | null): ListNode | null {
+    function reserve(tail, head) {
+        if (head === null) {
+            return tail;
+        }
+        let tmp = head.next;
+        head.next = tail;
+        tail = head;
+        return reserve(tail, tmp)
+    }
+    return reserve(null, head)
+};
+```
+# 两两交换链表中的节点
+示例 1：
+输入：head = [1,2,3,4]
+输出：[2,1,4,3]
+
+示例 2：
+输入：head = []
+输出：[]
+
+示例 3：
+输入：head = [1]
+输出：[1]
+```ts
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     val: number
+ *     next: ListNode | null
+ *     constructor(val?: number, next?: ListNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.next = (next===undefined ? null : next)
+ *     }
+ * }
+ */
+
+function swapPairs(head: ListNode | null): ListNode | null {
+    let virHead = new ListNode();
+    virHead.next = head;
+    let cur = virHead;
+    while (cur.next && cur.next.next) {
+        let temp = cur.next;
+        let temp2Next = cur.next.next.next;
+        cur.next = temp.next;
+        temp.next.next = temp;
+        temp.next = temp2Next;
+        cur = cur.next.next
+    }
+    return virHead.next
+};
+```
+
+# 删除链表的倒数第N个节点
+输入：head = [1,2,3,4,5], n = 2 输出：[1,2,3,5] 示例 2：
+
+输入：head = [1], n = 1 输出：[] 示例 3：
+
+输入：head = [1,2], n = 1 输出：[1]
+```ts
+function removeNthFromEnd(head: ListNode | null, n: number): ListNode | null {
+    let times = 0;
+    const virHead = new ListNode();
+    virHead.next = head;
+    let tail = virHead;
+    let del = virHead;
+    while (times < n && tail?.next) {
+        tail = tail.next;
+        times++
+    }
+    if (times < n) return head;
+    while (tail.next) {
+        del = del.next;
+        tail = tail.next;
+    }
+    del.next = del.next.next
+    return virHead.next;
+};
+```
+# 链表相交
+![32TO.jpeg](https://img.ocer.cc/images/2024/02/21/32TO.jpeg)
+```js
+var getIntersectionNode = function (headA, headB) {
+    let curA = headA;
+    let curB = headB;
+    let sizeA = 0, sizeB = 0;
+    while (curA?.next) {
+        curA = curA.next;
+        sizeA++
+    }
+    while (curB?.next) {
+        curB = curB.next;
+        sizeB++
+    }
+    const diffNum = Math.abs(sizeA - sizeB);
+    curA = headA;
+    curB = headB;
+    if (sizeA >= sizeB) {
+        for (let n = 0; n < diffNum; n++) {
+            curA = curA.next;
+        }
+    } else {
+        for (let n = 0; n < diffNum; n++) {
+            curB = curB.next;
+        }
+    }
+    while (curA !== curB) {
+        curA = curA?.next;
+        curB = curB?.next;
+    }
+    return curA;
+};
+```
+# 环形链表II
+![39SV.jpeg](https://img.ocer.cc/images/2024/02/21/39SV.jpeg)
+```ts
+function detectCycle(head: ListNode | null): ListNode | null {
+    let fast = head, slow = head;
+    while (fast !== null && fast.next !== null) {
+        fast = fast.next.next;
+        slow = slow.next;
+        if (fast === slow) {
+            let index1 = head;
+            let index2 = fast;
+            while (index1 !== index2) {
+                index1 = index1.next;
+                index2 = index2.next;
+            }
+            return index2
+        }
+    }
+    return null;
+};
+```