merge two sorted lists， 合并两个有序序列

/**
* 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) {
ListNode dumy = new ListNode(0);
ListNode head = dumy;
while(l1 != null && l2 != null)
{
if(l1.val < l2.val)
{
dumy.next = l1;
l1 = l1.next;
}
else
{
dumy.next = l2;
l2 = l2.next;
}
dumy = dumy.next;
}
if(l1 == null)
{
dumy.next = l2;
}
if(l2 == null)
{
dumy.next = l1;
}
return head.next;
}
}