方法：遍历

/**
 * 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==nullptr || headB==nullptr){
            return nullptr;
        }
        ListNode* A=headA;
        ListNode* B=headB;
        while(A!=B){
            A = A==nullptr?headB:A->next;
            B = B==nullptr?headA:B->next;
        }

        return A;
    }
};