输入两个递增排序的链表，合并这两个链表并使新链表中的节点仍然是递增排序的。
示例1：
输入：1->2->4, 1->3->4
输出：1->1->2->3->4->4
限制：
0 <= 链表长度 <= 1000
代码：
/**
* Definition for singly-linked list.
* public class ListNode {
* int val;
* ListNode next;
* ListNode(int x) { val = x; }
* }
*/
class Solution {
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
if(l1==null)
{
return l2;
}
if(l2==null)
{
return l1;
}
ListNode head = new ListNode(0);
ListNode result = head;
while(l1!=null&&l2!=null)
{
if(l1.val<=l2.val)
{
result.val = l1.val;
l1 = l1.next;
}
else
{
result.val = l2.val;
l2 = l2.next;
}
ListNode p = new ListNode(0);
result.next = p;
result = p;
}
if(l1!=null)
{
result.val = l1.val;
result.next = l1.next;
}
if(l2!=null)
{
result.val = l2.val;
result.next = l2.next;
}
return head;
}
}
