LeetCode 106. Construct Binary Tree from Inorder and Postorder Traversal

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题目

Given inorder and postorder traversal of a tree, construct the binary tree.

Note:

You may assume that duplicates do not exist in the tree.

For example, given

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inorder = [9,3,15,20,7]
postorder = [9,15,7,20,3]

Return the following binary tree:

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3
4
5
  3
 / \
9  20
  /  \
 15   7

思路

Recursion.

代码

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# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
    def buildTree(self, inorder, postorder):
        """
        :type inorder: List[int]
        :type postorder: List[int]
        :rtype: TreeNode
        """
        if not inorder or not postorder:
            return None
        val = postorder[-1]
        root = TreeNode(val)
        index = inorder.index(val)
        root.left = self.buildTree(inorder[:index], postorder[:index])
        root.right = self.buildTree(inorder[index+1:], postorder[index:-1])
        return root