Build a binary tree based on the forward and middle order of Python & re-build the binary tree based on the middle and back order, and output the results of the previous, middle, and post-order traversal.

This is based on my other C language version using Python implementation, added according to the central order and the post order re-built binary tree function, more detailed explanation can refer to: http://blog.csdn.net/hinyunsin/archive/2011/04/11/6315502.aspx

 

The following is the Python code:

#-*-Coding: UTF-8-*-<br/> #! /Usr/bin/python <br/> # filename: btreenode. PY <br/> ''' <br/> created on 2011-4-11 <br/> @ Author: Boyce <br/> @ Contact: boyce.ywr@gmail.com <br/> @ version: 1.0 <br/> ''' <br/> class btree: <br/> ''' <br/> represent a no in a binary tree. <br/> ''' <br/> def _ init _ (self, c = '/0', L = none, r = none ): <br/> ''' <br/> initializes the node's data <br/> ''' <br/> self. E = C <br/> self. left = L <br/> self. right = r <br/> def preordertraverse (BT ): <br/> ''' <br/> returns the result of the forward traversal <br/> ''' <br/> If BT: <br/> return '% S % s' % (BT. e, preordertraverse (BT. left), preordertraverse (BT. right) <br/> return ''<br/> def inordertraverse (BT ): <br/> ''' <br/> returns the result of the Middle-order traversal <br/> ''' <br/> If BT: <br/> return '% S % s' % (inordertraverse (BT. left), BT. e, inordertraverse (BT. right) <br/> return ''; <br/> def postordertraverse (BT ): <br/> ''' <br/> returns the result of post-sequential traversal. <br/> ''' <br/> If BT: <br/> return '% S % s' % (postordertraverse (BT. left), postordertraverse (BT. right), BT. e) <br/> return ''<br/> def printbtree (BT, depth): <br/> ''' <br/> Print the binary tree recursively, * indicates that the node is null. <br/> ''' <br/> if not BT: <br/> CH = '*' <br/> else: <br/> CH = BT. E <br/> ''' <br/> # Ch = (lambda X: (x and X. e) or '*') (BT) <br/> CH = BT. e if BT else '*' <br/> If (depth> 0): <br/> Print '% S % s' % (depth-1) * '', '--', CH) <br/> else: <br/> Print ch <br/> if not BT: <br/> return <br/> printbtree (BT. left, depth + 1) <br/> printbtree (BT. right, depth + 1) <br/> def buildbtreefromprein (preo, Ino ): <br/> ''' <br/> reconstruct the binary tree based on the pre-order and mid-order traversal results <br/> ''' <br/> If (preo = ''or ino = ''): <br/> return none <br/> Pos = ino. find (preo [0]) <br/> If (Pos <0): <br/> return none <br/> return btree (preo [0], buildbtreefromprein (preo [1: POS + 1], iNO [0: POS]), buildbtreefromprein (preo [POS + 1:], iNO [POS + 1:]) <br/> # Return nd <br/> def buildbtreefrominpost (Ino, po ): <br/> ''' <br/> reconstruct the binary tree based on the result of the central and backward traversal. <br/> ''' <br/> If (ino = ''or po = ''): <br/> return none <br/> Pos = ino. find (po [-1]) <br/> If (Pos <0): <br/> return none <br/> return btree (po [-1], buildbtreefrominpost (ino [0: POS], po [0: POS]), buildbtreefrominpost (ino [POS + 1:], po [pos:-1]) </P> <p> If _ name _ = '_ main __': <br/> preo = 'abdgcef' <br/> ino = 'dgbaechf '<br/> po = 'gdbehfca' <br/> bt = buildbtreefromprein (preo, Ino) <br/> Print 'build from preorder & inorder' <br/> Print 'preorder: % s' % (preordertraverse (BT) <br/> Print 'inorder: % s' % (inordertraverse (BT) <br/> Print 'storder: % s' % (postordertraverse (BT )) <br/> Print 'the btree is (* means no such a node): '<br/> printbtree (BT, 0) <br/> bt = buildbtreefrominpost (Ino, po) <br/> Print 'build from inorder & postorder' <br/> Print 'preorder: % s' % (preordertraverse (BT) <br/> Print 'inorder: % s' % (inordertraverse (BT) <br/> Print 'storder: % s' % (postordertraverse (BT )) <br/> Print 'the btree is (* means no such a node): '<br/> printbtree (BT, 0) <br/>

Python is really interesting. It is much simpler to write than C. Of course, I am actually far from concise enough. I can't help it. I am a newbie ~

Here, the function of rebuilding a binary tree in the middle and back order is added. The principle is the same as that in the pre-order and Middle-order reconstruction.

 

The execution result is as follows: