---
title: leetcode - Reverse Linked List
date: 2023-02-18
public: true
summary: 反转链表，这次你一定要懂
tags:
    - Reverse Linked List
    - 反转链表
    - leetcode
---

> [Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/description/)，这个不会建议回炉重造了(说的就是我)。

## recursive

```typescript
/**
 * 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 {
  if (head === null || head.next === null) return head;
  const newHead = reverseList(head.next);
  head.next.next = head;
  head.next = null;
  return newHead;
};
```

## two pointers

```typescript
/**
 * 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 prev = null;
  let curr = head;
  let next = null;
  while (curr !== null) {
    next = curr.next;
    curr.next = prev;
    prev = curr;
    curr = next;
  }
  return prev;
};
```




leetcode - Reverse Linked List

---
title: leetcode - Reverse Linked List
date: 2023-02-18
public: true
summary: 反转链表，这次你一定要懂
tags:
    - Reverse Linked List
    - 反转链表
    - leetcode
---

> [Reverse Linked List](https://leetcode.com/problems/reverse-linked-list/description/)，这个不会建议回炉重造了(说的就是我)。

## recursive

```typescript
/**
 * 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 {
  // base case, breaking recursive loop
  if (head === null || head.next === null) return head;
  const newHead = reverseList(head.next);
  head.next.next = head;
  head.next = null;
  return newHead;
};
```

## two pointers

```typescript
/**
 * 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 prev = null;
  let curr = head;
  let next = null;
  while (curr !== null) {
    next = curr.next;
    curr.next = prev;
    prev = curr;
    curr = next;
  }
  return prev;
};
```




leetcode - Reverse Linked List @ Sat, Feb 18, 2023 9:53 PM		leetcode - Reverse Linked List @ Sun, Feb 19, 2023 9:27 AM
	Expand 26 lines ...
27	`*/`	27		`*/`
28		28
29	`function reverseList(head: ListNode \| null): ListNode \| null {`	29		`function reverseList(head: ListNode \| null): ListNode \| null {`
		30	+	`// base case, breaking recursive loop`
30	`if (head === null \|\| head.next === null) return head;`	31		`if (head === null \|\| head.next === null) return head;`
31	`const newHead = reverseList(head.next);`	32		`const newHead = reverseList(head.next);`
32	`head.next.next = head;`	33		`head.next.next = head;`
	Expand 33 lines ...