1 # Definition for a binary tree node.
 2 # class TreeNode(object):
 3 #     def __init__(self, x):
 4 #         self.val = x
 5 #         self.left = None
 6 #         self.right = None
 7 
 8 class Solution(object):
 9     def bstFromPreorder(self, preorder):
10         """
11         :type preorder: List[int]
12         :rtype: TreeNode
13         """
14         if len(preorder)==0: return None
15         if len(preorder)==1: return TreeNode(preorder[0])
16         
17         root = TreeNode(preorder[0])
18         idx=1
19         while idx<len(preorder) and preorder[idx]<preorder[0]:
20             idx+=1
21         root.left = self.bstFromPreorder(preorder[1:idx])
22         root.right = self.bstFromPreorder(preorder[idx:])
23         return root
24 
25