# Line 48: AttributeError: 'list' object has no attribute 'val'

• ``````# Definition for a binary tree node.
class TreeNode(object):
def __init__(self, x):
self.val = x
self.left = None
self.right = None

class Solution(object):
def buildTree(self, preorder, inorder):
"""
:type preorder: List[int]
:type inorder: List[int]
:rtype: TreeNode
"""
if len(preorder)==0:
return []
root=TreeNode(preorder[0])

if len(preorder)==1:
return root

rootInIdx=inorder.index(preorder[0])
# preorder[lastNodeInLeftIdx] is the largest number in left subtree
lastNodeInLeftIdx=preorder.index(inorder[rootInIdx-1])

root.left=self.buildTree(preorder[1:lastNodeInLeftIdx+1],inorder[:rootInIdx])
root.right=self.buildTree(preorder[lastNodeInLeftIdx+1:],inorder[rootInIdx+1:])

return root

a=Solution()
print a.buildTree([1,2],[2,1]).val
print a.buildTree([1,2],[2,1]).left.val
print a.buildTree([1,2],[2,1]).right
``````

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