题目：

示例 1：

示例 2：

# Definition for singly-linked list.
# class ListNode:
# def __init__(self, x):
# self.val = x
# self.next = None
class Solution:
    def isPalindrome(self, head: ListNode) -> bool:
        judge = []
        while head:
            judge.append(head.val)
            head = head.next
        return judge == judge[::-1]

# Definition for singly-linked list.
# class ListNode:
# def __init__(self, x):
# self.val = x
# self.next = None
class Solution:
    def isPalindrome(self, head: ListNode) -> bool:
        i ,length= head, 0
        if not head:
            return 1 == 1
        while i:
            length += 1
            i = i.next
        stack = []
        r = head
        k = length//2
        if length % 2 != 0:
            k+=1
        for x in range (k):
            stack.append(r.val)
            r = r.next
            if length % 2 != 0 and x == length//2:
                stack.pop()
        for j in reversed(stack):
            if j == r.val:
                stack.pop()
            r = r.next
        return len(stack) == 0