/**
 * 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* head = new ListNode(0);
        ListNode *cur = head;
        while(l1!=NULL && l2!=NULL)
        {
            if(l1->val < l2->val){
                cur->next=l1;
                l1=l1->next;
            }
            else{
                cur->next = l2;
                l2 = l2->next;
            }
            cur = cur->next;
        }
        cur ->next = (l1 !=NULL ? l1 : l2);
        return head->next;
    }
};