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| class Solution(object):
def buildTree(self, inorder, postorder):
"""
:type inorder: List[int]
:type postorder: List[int]
:rtype: TreeNode
"""
if len(inorder)== 0:
return None
root = TreeNode(postorder[-1])
indexInorder = inorder.index(postorder[-1])
root.right = self.buildTree(inorder[indexInorder+1:],postorder[indexInorder:-1])
root.left = self.buildTree(inorder[:indexInorder],postorder[:indexInorder] )
return root
### The above code will cause out of memory error
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
# @param inorder, a list of integers
# @param postorder, a list of integers
# @return a tree node
def buildTree(self, inorder, postorder):
if not inorder: return None # inorder is empty
self.inorder, self.postorder = inorder, postorder
return self.dfs(0, 0, len(inorder))
def dfs(self, inLeft, postLeft, Len):
if Len <= 0:
return None
root = TreeNode(self.postorder[postLeft + Len - 1])
rootPos = self.inorder.index(self.postorder[postLeft + Len - 1])
root.left = self.dfs(inLeft, postLeft, rootPos - inLeft)
root.right = self.dfs(rootPos + 1, postLeft + rootPos - inLeft, Len - 1 - (rootPos - inLeft))
return root
|