输入：[8,5,1,7,10,12]输出：[8,5,10,1,7,null,12]
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
