两个链表的第一个公共结点

题目描述
输入两个链表，找出它们的第一个公共结点。

# -*- 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
        l1 = l2 = 0
        r1, r2 = pHead1, pHead2
        while r1: 
            r1 = r1.next
            l1 += 1
        while r2: 
            r2 = r2.next
            l2 += 1
        
        r1, r2 = pHead1, pHead2
        if l1>l2:
            for _ in range(l1-l2): r1=r1.next
        else:
            for _ in range(l2-l1): r2=r2.next
        
        while r1!=r2:
            r1, r2 = r1.next, r2.next
        return r1