Intersection of Two Linked Lists

题目描述：

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.

时间复杂度和空间复杂度都有限制。

如果两个有重叠，重叠部分的长度肯定是相等的。那就接去较长链表多余的部分，然后一个一个比较，若相等则是交叉点。

代码如下：