Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

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