21. Merge Two Sorted Lists(C++)

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.

Solution 

 1 /**
 2  * Definition for singly-linked list.
 3  * struct ListNode {
 4  *     int val;
 5  *     ListNode *next;
 6  *     ListNode(int x) : val(x), next(NULL) {}
 7  * };
 8  */
 9 class Solution {
10 public:
11     ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
12         ListNode res(INT_MIN);
13         ListNode *p=&res;
14         while(l1&&l2){
15             if(l1->val>l2->val){
16                 p->next=l2;
17                 l2=l2->next;
18             }else{
19                 p->next=l1;
20                 l1=l1->next;
21             }
22             p=p->next;
23         }
24         p->next=l1?l1:l2;
25         return res.next;
26     }
27 };