两个链表公共结点

题目描述
输入两个链表，找出它们的第一个公共结点。（注意因为传入数据是链表，所以错误测试数据的提示是用其他方式显示的，保证传入数据是正确的）

# -*- coding:utf-8 -*-
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class Solution:
    def FindFirstCommonNode(self, pHead1, pHead2):
        # write code here
        while pHead1 == None:
            return None
        while pHead2 == None:
            return None
        pTemp1 = pHead1
        pTemp2 = pHead2
        
        stack1 = []
        stack2 = []
        # 把两个链表都压入栈
        while pTemp1:
            stack1.append(pTemp1)
            pTemp1 = pTemp1.next
        while pTemp2:
            stack2.append(pTemp2)
            pTemp2 = pTemp2.next
            
        p = None
        # 由于相同节点后的所有节点都相同，所以倒着弹栈，一直到不相等，就为第一个相同的节点
        while stack1 and stack2 and stack1[-1] == stack2[-1]:
            p = stack1.pop()
            stack2.pop()
        return p