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

直接上代码：

 1 public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
 2         int lenA = getLength(headA);
 3         int lenB = getLength(headB);
 4         ListNode curA = headA;
 5         ListNode curB = headB;
 6         int count = lenA > lenB ? lenA - lenB : lenB - lenA;
 7         if (lenA > lenB) {
 8             for (int i = 0; i < count; i++) {
 9                 curA = curA.next;
10             }
11         }else{
12             for (int i = 0; i< count; i++) {
13                 curB = curB.next;
14             }
15         }
16         while (curA != null && curB != null) {
17             if (curA.val == curB.val) {
18                 return curA;
19             }
20             curA = curA.next;
21             curB = curB.next;
22         }
23         return null;
24     }
25     
26     private int getLength(ListNode head) {
27         ListNode dummy = new ListNode(0);
28         ListNode cur = dummy;
29         dummy.next = head;
30         int count = 0;
31         while (cur != null) {
32             cur = cur.next;
33             count++;
34         }
35         return count;
36     }