重建二叉树.py

'''
输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。假设输入的前序遍历和中序遍历的结果中都不含重复的数字。例如输入前序遍历序列{1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建二叉树并返回。


'''


# -*- 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) == 1 or len(tin) == 1: return TreeNode(pre[0])
        root = TreeNode(pre[0])
        for i, n in enumerate(tin):
            if n == root.val:
                root.left = self.reConstructBinaryTree(pre[1:i + 1], tin[:i])
                root.right = self.reConstructBinaryTree(pre[i + 1:], tin[i + 1:])
        return root