打平一个单链表 (Flatten a single linked list)

我的代码:

public Node flatten(Node head){
 if(head==null) return null;
 Node tree = head.right;
 if(head.left!=null){
  head.right = head.left;
  head.left = null;
  head = flatten(head.right);
 }

 if (tree!=null) {
  head.right = tree
  head = flatten(head.right);
 }

 return head;
}