/**

 * Definition for singly-linked list.

 * struct ListNode {

 *     int val;

 *     ListNode *next;

 *     ListNode(int x) : val(x), next(NULL) {}

 * };

 */

class Solution {

public:

    ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {

        ListNode *cur_headA=headA;

        ListNode *cur_headB=headB;

        int num_headA=;

        int num_headB=;

        while(cur_headA!=NULL)//统计headA个数

        {

            num_headA++;

            cur_headA=cur_headA->next;

        }

        while(cur_headB!=NULL)//统计headB个数

        {

            num_headB++;

            cur_headB=cur_headB->next;

        }

        if(num_headA*num_headB==)//如果有一个为NULL，返回NULL

            return NULL;

        if(num_headA>num_headB)//不妨设headA的个数大于headB

        {

            cur_headA=headA;

            cur_headB=headB;

        }

        else

        {

            cur_headA=headB;

            cur_headB=headA;

        }

        int temp=abs(num_headA-num_headB);//让headA的指针先走到和headB的开头相同的位置

        while(temp>)

        {

            cur_headA=cur_headA->next;

            temp--;

        }

        if(cur_headA==cur_headB)//如果已经相同，直接返回

            return cur_headA;

        while(cur_headA->next!=cur_headB->next)//一直往后走，最差也就走到头NULL

        {

            cur_headA=cur_headA->next;

            cur_headB=cur_headB->next;

        }

        return cur_headA->next;

    }

};