[LeetCode] #21 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.

本题就是简单的链表合成。时间：14ms

我的代码：

/**
* 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) {
        if (l1 == NULL)
            return l2;
        if (l2 == NULL)
            return l1;
        ListNode *p1, *p2, *pHead, *pNext;
        p1 = l1, p2 = l2, pHead = pNext;
        while (p1!=NULL&&p2!=NULL){
            if (p1->val <= p2->val){
                pNext->next = p1;
                p1 = p1->next;
            }
            else{
                pNext->next = p2;
                p2 = p2->next;
            }
            pNext = pNext->next;
        }
        while (p1!=NULL){
            pNext->next = p1;
            p1 = p1->next;
            pNext = pNext->next;
        }
        while (p2!=NULL){
            pNext->next = p2;
            p2 = p2->next;
            pNext = pNext->next;
        }
        return pHead->next;
    }
};