合并两个排序的链表 C++实现

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* merge(ListNode* l1, ListNode* l2) {
        ListNode* res=new ListNode(-1);
        ListNode* tail=res;
        while(l1 && l2){
            if(l1->valval){
                tail=tail->next=l1;
                l1=l1->next;
            }else{
                tail=tail->next=l2;
                l2=l2->next;
            }
         }
        while(l1) {
            tail=tail->next=l1;
            l1=l1->next;
        }
        while(l2)  {
            tail=tail->next=l2;
            l2=l2->next;
        }
        return res->next;
    }
};