题解 | #两个链表的第一个公共结点#

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

#
# 
# @param pHead1 ListNode类 
# @param pHead2 ListNode类 
# @return ListNode类
#
class Solution:
    def FindFirstCommonNode(self , pHead1 , pHead2 ):
        # write code here
        # 改进了下以前的高赞回答，以前的测试用例可能都是非空链表以及肯定有公共结点
        # 所以直接复制以前的高赞回答不通过
        if not pHead1 or not pHead2:
            return None
        l1, l2 = pHead1, pHead2
        count_null = {}
        while l1 != l2:
            if not l1.next:
                count_null['l1'] = count_null.get('l1', 0) + 1
                l1 = pHead2
            else:
                l1 = l1.next
            if not l2.next:
                count_null['l2'] = count_null.get('l2', 0) + 1
                l2 = pHead1
            else:
                l2 = l2.next
            if count_null.get('l1') == 2 and count_null.get('l2') == 2:
                # 如果各自都走到了链表末端两次都没有碰上，则可以说明没有公共节点
                return None
        return l1