檢查鏈表是否爲迴文 python實現

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

'''
題目描述

請編寫一個函數，檢查鏈表是否爲迴文。

給定一個鏈表ListNode* pHead，請返回一個bool，代表鏈表是否爲迴文。
測試樣例：

{1,2,3,2,1}

返回：true

{1,2,3,2,3}

返回：false

@author chimuuu
'''

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

class Palindrome:
    def isPalindrome(self, pHead):
        # write code here
        if pHead == None or pHead.next == None:
            return True

        pslow = pHead
        pfast = pHead
        stack = [pslow.val]
        # 查找鏈表中心
        while True:
            # 奇數鏈，比較從後半部分第一個開始
            if not pfast.next:
                mid = pslow
                break
            # 偶數鏈，比較從後半部分第一個開始
            elif pfast and not pfast.next.next:
                mid = pslow.next
                break
            pslow = pslow.next
            pfast = pfast.next.next
            stack.append(pslow.val)


        # 迴文對比
        print stack
        while stack and mid.next:
            tmp = stack.pop()
            if mid.val != tmp:
                return False

            print mid.val, tmp
            mid = mid.next
        return True

node1 = ListNode(1)
node2 = ListNode(2)
node3 = ListNode(3)
# node4 = ListNode(3)
node5 = ListNode(2)
node6 = ListNode(1)
node1.next = node2
node2.next = node3
node3.next = node5
# node4.next = node5
node5.next = node6


S = Palindrome()
p = S.isPalindrome(node1)
print(p)