剑指offer——重建二叉树

# -*- coding:utf-8 -*-
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class Solution:
    # 返回构造的TreeNode根节点
    def reConstructBinaryTree(self, pre, tin):
        # write code here
        if len(pre)==0 or len(tin)==0:
            return None
        if len(pre)==len(tin)==1:
            root= TreeNode(pre[0])
            return root
        
        root=TreeNode(pre[0])
        index=tin.index(root.val)
        
        tin_left=tin[:index]
        tin_right=tin[index+1:]
        
        left_length=len(tin_left)
        pre_left=pre[1:left_length+1]
        pre_right=pre[left_length+1:]
        
        root.left=self.reConstructBinaryTree(pre_left,tin_left)
        root.right=self.reConstructBinaryTree(pre_right,tin_right)
        return root