21 Merge Two Sorted Lists(两链表归并排序Easy)

题目意思：对两个递增链表进行归并排序

思路：没什么好说的，二路归并

 /**
  * 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* head=new ListNode();
         ListNode* p=head;
         while(l1&&l2){
             if(l1->val<=l2->val){
                 p->next=l1;
                 l1=l1->next;
                 p=p->next;
             }
             else{
                 p->next=l2;
                 l2=l2->next;
                 p=p->next;
             }
         }
         if(l1)p->next=l1;
         if(l2)p->next=l2;
         return head->next;    //第一个节点去掉
     }
 };