Merge Two Sorted Lists

      class Solution {

public:

    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {

        ListNode *helper=new ListNode(0);

        ListNode *head=helper;

        while(l1 && l2)

        {

             if(l1->val<l2->val) helper->next=l1,l1=l1->next;

             else helper->next=l2,l2=l2->next;

             helper=helper->next;

        }

        if(l1) helper->next=l1;

        if(l2) helper->next=l2;

        return head->next;

    }

};