LeetCode OJ：Intersection of Two Linked Lists（两个链表的插入）

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.

找出第一个合并的节点的位置（或者说插入），注意复杂度为O(N)，那么先遍历两个链表，求出长度，把长的那个链表前面的“剪去”,下面的就好比较了，代码如下：

 1 class Solution {
 2 public:
 3     ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
 4         int len1, len2;
 5         len1 = len2 = 0;
 6         ListNode * p = headA;
 7         ListNode * q = headB;
 8         while(p){
 9             p = p->next;
10             len1++;
11         }
12         while(q){
13             q = q->next;
14             len2++;
15         }
16         if(len1 > len2){
17             int diff = len1 - len2;
18             while(diff--)
19                 headA = headA->next;
20         }else if(len2 > len1){
21             int diff = len2 - len1;
22             while(diff--)
23                 headB = headB->next;
24         }
25         while(headA){
26             if(headA == headB)
27                 return headA;
28             headA = headA->next;
29             headB = headB->next;
30         }
31         return NULL;
32     }
33 };