# 回文链表

<p>给你一个单链表的头节点 <code>head</code> ，请你判断该链表是否为回文链表。如果是，返回 <code>true</code> ；否则，返回 <code>false</code> 。</p>

<p>&nbsp;</p>

<p><strong>示例 1：</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/03/03/pal1linked-list.jpg" style="width: 422px; height: 62px;" />
<pre>
<strong>输入：</strong>head = [1,2,2,1]
<strong>输出：</strong>true
</pre>

<p><strong>示例 2：</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/03/03/pal2linked-list.jpg" style="width: 182px; height: 62px;" />
<pre>
<strong>输入：</strong>head = [1,2]
<strong>输出：</strong>false
</pre>

<p>&nbsp;</p>

<p><strong>提示：</strong></p>

<ul>
	<li>链表中节点数目在范围<code>[1, 10<sup>5</sup>]</code> 内</li>
	<li><code>0 &lt;= Node.val &lt;= 9</code></li>
</ul>

<p>&nbsp;</p>

<p><strong>进阶：</strong>你能否用&nbsp;<code>O(n)</code> 时间复杂度和 <code>O(1)</code> 空间复杂度解决此题？</p>


## template

```python
class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None


class Solution:
    def isPalindrome(self, head: ListNode) -> bool:

        lst = []

        node = head

        while node:
            lst.append(node.val)
            node = node.next

        start = 0
        end = len(lst) - 1

        while start < end:
            if lst[start] != lst[end]:
                return False
            start += 1
            end -= 1

        return True

```

## 答案

```python

```

## 选项

### A

```python

```

### B

```python

```

### C

```python

```