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.

代码如下:

 /**
  * Definition for singly-linked list.
  * public class ListNode {
  *     int val;
  *     ListNode next;
  *     ListNode(int x) { val = x; }
  * }
  */
 public class Solution {
     public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
         if(l1==null&&l2==null)
         return null;
         if(l1==null&&l2!=null)
         return l2;
         if(l1!=null&&l2==null)
         return l1;

         ListNode head=l1.val<=l2.val?l1:l2;
         ListNode p=head;
         if(head==l1)
         l1=l1.next;
         else if(head==l2)
         l2=l2.next;

         while(l1!=null&&l2!=null)
         {
             head.next=l1.val<=l2.val?l1:l2;
         if(head.next==l1)
         l1=l1.next;
         else if(head.next==l2)
         l2=l2.next;
         head=head.next;
         }

         if(l1==null&&l2==null)
         head.next=null;
         if(l2!=null)
         head.next=l2;
         if(l1!=null)
         head.next=l1;

         return p;
     }
 }