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
#
# 设置两个指针，分别以同样的速度遍历两个链表。当两个指针在同一个节点相遇时，说明这个节点就是第一个公共节点
# 当两个指针经过多轮遍历，最后同时回到了两个链表头时，说明没有公共节点
class Solution:
    def FindFirstCommonNode(self , pHead1 , pHead2 ):
        node1, node2 = pHead1, pHead2
        if node1 == None or node2 == None:
            return None
        
        count = 0
        while True:
            if node1 == None:
                node1 = pHead1
            if node2 == None:
                node2 = pHead2
            if node1 == node2:
                return node1
            elif node1 == pHead1 and node2 == pHead2 and count != 0:
                return None
            node1 = node1.next
            node2 = node2.next
            count += 1