/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
ListNode *findFirstCommonNode(ListNode *headA, ListNode *headB) {
auto p=headA,q=headB;
//有没有公共点,交换走下来总会相遇
while(p!=q){
if(p)p=p->next;//正常往后走
else p=headB;//走到空节点,从另一端开始
if(q)q=q->next;
else q=headA;
}
return q;
}
};