[Leetcode] Merge Two Sorted Lists

 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;
13         ListNode *p = new ListNode(0);
14         res = p;
15         while (l1 != NULL && l2 != NULL) {
16             if (l1->val < l2->val) {
17                 p->next = l1;
18                 l1 = l1->next;
19             } else {
20                 p->next = l2;
21                 l2 = l2->next;
22             }
23             p = p->next;
24         }
25         if (l1 != NULL) {
26             p->next = l1;
27         }
28         if (l2 != NULL) {
29             p->next = l2;
30         }
31         return res->next;
32     }
33 };