# _*_ coding: utf-8 _*_


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


class Solution(object):
    def isPalindrome(self, head):
        """
        :type head: ListNode
        :rtype: bool
        """
        if not head or not head.next:
            return True
        if not head.next.next:
            if head.val == head.next.val:
                return True
            else:
                return False
        slow = head
        fast = head.next
        pre_node = None
        while fast and fast.next:
            fast = fast.next.next
            # 反转链表
            temp = slow.next
            slow.next = pre_node
            pre_node = slow
            slow = temp
            
        # 节点个数为偶数
        if fast:
            l2 = slow.next
            slow.next = pre_node
            l1 = slow
        else:
            l1 = pre_node
            l2 = slow.next
        
        while l1:
            if l1.val != l2.val:
                return False
            l1, l2 = l1.next, l2.next
        return True