52.两个链表的第一个公共节点

双指针

/**
 * 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) {
        if(!headA||!headB)return NULL;
        ListNode *l1,*l2;
       l1=headA;
       l2=headB;
       while(l1!=l2)
       {
           l1 = l1==NULL?headB:l1->next;
           l2 = l2==NULL?headA:l2->next;
       }
       return l1;
    }
};