如何在java中获取LinkedList的head节点

Question

这是leetcode 21合并两个链表的问题，我尝试了下面给出的最佳解决方案但我还是犯了错误？

class Solution {
public ListNode mergeTwoLists(ListNode l1, ListNode l2) 
{
ListNode one = l1.head;
ListNode two = l2.head;

LinkedList res=new LinkedList();

while(one.val!= null && two.val!= null)
{
if(one.val<=two.val)
{
res.addLast(one.val);
one=one.next;
}
else
{
res.addLast(two.val);
two=two.next;
}
}
//if second list finish
while(one.val!=null)
{
res.addLast(one.val);
one=one.next;
}
//if first list finish
while(two.val!=null)
{
res.addLast(two.val);
two=one.next;
}


return res;




}
}

第14行：错误：找不到符号符号：可变头

我们如何访问链接列表的标题？

Answer 1

我们也可以递归地执行：

public class Solution {
public static final ListNode mergeTwoLists(
final ListNode l1, 
final ListNode l2
) {
if (l1 == null) {
return l2;
}
if (l2 == null) {
return l1;
}
final ListNode merged;
if (l1.val < l2.val) {
merged = l1;
merged.next = mergeTwoLists(l1.next, l2);
} else {
merged = l2;
merged.next = mergeTwoLists(l1, l2.next);
}
return merged;
}
}