Description

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。

Solutions

# -*- coding:utf-8 -*-
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class Solution:
    def find_idx(self, nums, target):
        for i in range(len(nums)):
            if nums[i] == target:
                return i
    
    # 返回构造的TreeNode根节点
    def reConstructBinaryTree(self, pre, tin):
        # write code here
        if pre == [] or tin == []:
            return None
        root_val = pre[0]
        root_idx = self.find_idx(tin, root_val)
        root = TreeNode(root_val)

        root.left = self.reConstructBinaryTree(pre[1:root_idx+1], tin[:root_idx])
        root.right = self.reConstructBinaryTree(pre[root_idx+1:], tin[root_idx+1:])
        return root

References

  1. 重建二叉树