每天一道python练习11

题目: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.

思路:利用二叉树遍历的规则进行重组

code:

# -*- 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

        rootValue = pre[0]
        root = TreeNode(rootValue)
        if len(pre)==1:
            return root
        rootTinIndex = 0
        for i in range(len(tin)):
            if tin[i] == rootValue:
                rootTinIndex = i
        preStart = 1
        preEnd = rootTinIndex+1
        tinStart = 0
        tinEnd = rootTinIndex
        if rootTinIndex > 0:
            root.left = self.reConstructBinaryTree(pre[preStart:preEnd], tin[tinStart:tinEnd])
        if rootTinIndex < len(pre):
            root.right = self.reConstructBinaryTree(pre[preEnd:], tin[tinEnd+1:])
        return root