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：

 class Solution {
 public:
     ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
         int len1, len2;
         len1 = len2 = ;
         ListNode * p = headA;
         ListNode * q = headB;
         while(p){
             p = p->next;
             len1++;
         }
         while(q){
             q = q->next;
             len2++;
         }
         if(len1 > len2){
             int diff = len1 - len2;
             while(diff--)
                 headA = headA->next;
         }else if(len2 > len1){
             int diff = len2 - len1;
             while(diff--)
                 headB = headB->next;
         }
         while(headA){
             if(headA == headB)
                 return headA;
             headA = headA->next;
             headB = headB->next;
         }
         return NULL;
     }
 };