# 206. Reverse Linked List

## 1.問題

* 反轉linked list

![](https://901207480-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LGKoChvN9am4__HCIRK%2F-LJaD8i6Ctb1QYbROw6s%2F-LJaMCWxjTOgr_yXVVB9%2F2018081101.jpg?alt=media\&token=ccac1e46-9a7b-453c-a0c0-fad371d04434)

## 2.想法

* 提問
  * 確認題意:  反轉linked list
* function header, parameter
* test input
* 說明想法
  * 三個指標
    * current: 指向head, 下一回合時移到next
    * next: 指向head->next, 並讓current移動
    * pre: 一開始指向NULL, 並讓head->next移動
* 測試計算複雜度

## 3.程式碼

```
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        if (head == NULL)
        {
            return NULL;
        }
        
        ListNode *prev = head;
        ListNode *curr = head->next;
        prev->next = NULL;
        
        while (curr != NULL)
        {
            ListNode *next = curr->next;
            curr->next = prev;
            prev = curr;
            curr = next;
        }
        return prev;
    }
};
```

## 4.Performance

![](https://901207480-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LGKoChvN9am4__HCIRK%2F-LJaD8i6Ctb1QYbROw6s%2F-LJaMS8S-cnHVNFydgrC%2F2018081102.jpg?alt=media\&token=de2f9341-658f-487f-a535-be72d73b5eb2)


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://jenhsuan.gitbook.io/algorithm/leetcode/206.-reverse-linked-list.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.