merge-two-sorted-lists

题目：

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.

程序：

class Solution {public:    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {        if(l1==NULL)            return l2;        if(l2==NULL)            return l1;        ListNode dummy(-1);//定义头指针        ListNode *p=&dummy;        for(;l1!=NULL&&l2!=NULL;p=p->next){            if(l1->val>l2->val){                p->next=l2;                l2=l2->next;            }            else{                p->next=l1;                l1=l1->next;            }        }        p->next=l1!=NULL?l1:l2;        return dummy.next;    }};