//模拟中序遍历构造二叉树
private TreeNode help(int begin,int end)
{
if (begin > end)//这里的判断很重要，跟数组很像
return null;
int mid = (begin + end) / 2;
TreeNode left=help(begin,mid-1);//按照中序遍历的顺序先构造左子树
TreeNode node = new TreeNode(current.val);
node.left = left;
current = current.next;
node.right = help(mid + 1, end);//再构造右子树
return node;
}
public TreeNode SortedListToBST(ListNode head)
{
current = head;
int length = 0;
while (head != null)
{
length++;
head = head.next;
}
if (length == 0)
return null;
return help(1,length);
}
