LeetCode-Intersection of Two Linked Lists

Write a program to find the node at which the intersection of two singly linked lists begins.

For example, the following two linked lists:

A:          a1 → a2
↘
c1 → c2 → c3
↗
B:     b1 → b2 → b3

begin to intersect at node c1.

Notes:
If the two linked lists have no intersection at all, return 

null

.
The linked lists must retain their original structure after the function returns.
You may assume there are no cycles anywhere in the entire linked structure.

Your code should preferably run in O(n) time and use only O(1) memory.
题目意思：给定两个链表，找到他们的第一个公共节点；
解题思路：先确定两个链表节点个数的差，然后让两个指针间隔节点差同步向前，当遇到两个节点的val相等时为第一个公共节点；
代码如下：