01_从中序与后序遍历序列构造二叉树

# 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, inorder, postorder):
        """
        :type inorder: List[int]
        :type postorder: List[int]
        :rtype: TreeNode
        """
        if not inorder or not postorder:
            return
        root = TreeNode(postorder[-1])
        index = inorder.index(postorder[-1])
        # 要抛出根节点 形参的 inorder 和 postorder 长度要相等
        root.left = self.buildTree(inorder[:index], postorder[:index])
        # 中序根节点在index处 后序根节点在-1索引处
        root.right = self.buildTree(inorder[index+1:], postorder[index:-1])
        return root