題目:

輸入某二叉樹的前序遍歷和中序遍歷的結果，請重建出該二叉樹。假設輸入的前序遍歷和中序遍歷的結果中都不含重複的數字。例如輸入前序遍歷序列{1,2,4,7,3,5,6,8}和中序遍歷序列{4,7,2,1,5,3,8,6}，則重建二叉樹並返回。

連結：

思路：

解答：

# -*- coding:utf-8 -*-
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class
 
 Solution:
    # 返回構造的TreeNode根節點
    def reConstructBinaryTree(self, pre, tin):
        # write code here
        if not pre or not tin or len(pre) != len(tin): return
        return self.reconstruct(pre, tin, 0, len(pre)-1, 0, len(tin)-1)
    def reconstruct(self, pre, tin, preStart, preEnd, tinStart,
 
 tinEnd):
        rootValue = pre[preStart]
        rootIndex = tin.index(rootValue)
        root = TreeNode(rootValue)
        if preStart == preEnd:
            return root
        if rootIndex > tinStart:
            root.left = self.reconstruct(pre, tin, preStart + 1, rootIndex - tinStart + preStart,
 
 tinStart, rootIndex - 1)
        if tinEnd > rootIndex:
            root.right = self.reconstruct(pre, tin, rootIndex - tinStart + preStart + 1, preEnd, rootIndex + 1, tinEnd)
        return root