题目原型：
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.
直接贴代码吧：
public ListNode mergeTwoLists(ListNode l1, ListNode l2)
{
if(l1==null&&l2==null)
return null;
else if(l1==null)
return l2;
else if(l2==null)
return l1;
else
{
ListNode p,q,head,t;
p = l1;
q = l2;
head = p.val<=q.val?p:q;
while(p!=null&&q!=null)
{
if(p.val<=q.val)
{
t = p.next;
if(t!=null)
if(q.val<t.val)
{
p.next = q;
p = t;
}
else
{
p = t;
}
else
{
p.next = q;
break;
}
}
else
{
t = q.next;
if(t!=null)
if(p.val<=t.val)
{
q.next = p;
q = t;
}
else
{
q = t;
}
else
{
q.next = p;
break;
}
}
}
return head;
}