Four strategies for non-recursive traversal of Binary Trees-first, middle, last, and Sequence

Recursive Algorithms that traverse Binary Trees are easy to understand, but non-recursive loop algorithms are not easy to see at a glance. The following five algorithms are written according to Yan Weimin's "Data Structure" and USTC's instructor Zhang Yu's handout. Some of them have been modified.

 

First traverse Binary Tree Algorithm 1

// Copyright (c) 2009, Alex Zhong. all rights reserved. </P> <p> Status preordertraverse (bitree T, status (visit *) (telemtype E) <br/>{< br/> initstack (s ); <br/> push (S, T); <br/> P = T; // or gettop (S, P); <br/> while (! Stackempty (s) & P) <br/>{< br/> while (p) <br/>{< br/> If (! Visit (p-> data) <br/> return error; <br/> push (p-> rchild); <br/> P = p-> lchild; <br/>}< br/> POP (S, P); <br/>}< br/> destroystack (s); <br/> Return OK; <br/>}

 

First traverse binary tree algorithm 2

// Copyright (c) 2009, Alex Zhong. all rights reserved. </P> <p> Status preordertraverse (bitree T, status (visit *) (telemtype) <br/>{< br/> initstack (s ); <br/> push (S, T); <br/> P = T; <br/> while (! Stackempty (s) & P) <br/>{< br/> while (p) <br/>{< br/> If (! Visit (p-> data) <br/> return error; <br/> push (S, P); <br/> P = p-> lchild; <br/>}< br/> If (! Stackempty (s) <br/>{< br/> POP (S, P); <br/> P = p-> rchild; <br/>}< br/> destroystack (s); <br/> Return OK; <br/>}< br/>

 

Ordinal traversal Binary Tree Algorithm

// Copyright (c) 2009, Alex Zhong. all rights reserved. </P> <p> Status inordertraverse (bitree T, status (visit *) (telemtype E) <br/>{< br/> initstack (s ); <br/> push (S, T) '<br/> P = T; <br/> while (! Stackempty (s) & P) <br/>{< br/> while (p) <br/>{< br/> push (S, P ); <br/> P = p-> lchild; <br/>}< br/> POP (S, P); <br/> If (! Visit (p-> data) <br/> return error; <br/> P = p-> rchild; <br/>}< br/> destroystack (s ); <br/> Return OK; <br/>}

 

Post-order traversal Binary Tree Algorithm

// Copyright (c) 2009, Alex Zhong. all rights reserved. </P> <p> Status postordertraverse (bitree T, status (visit *) (telemtype E) <br/>{< br/> initstack (s ); <br/> push (S, T); <br/> P = T; <br/> while (! Stackempty (s) & P) <br/>{< br/> If (P) <br/> {// always go to the leftmost node <br/> push (S, P); <br/> P = p-> lchild; <br/>}< br/> else <br/> {// If P is null <br/> gettop (S, P ); <br/> If (p-> rchild & P-> rchild! = R) <br/> {// P: The right child with the right child or P is not just accessed <br/> P = p-> rchild; <br/> push (S, P); <br/> P = p-> lchild; <br/>}< br/> else <br/> {// P no right child or P right child has just been accessed <br/> POP (S, P ); <br/> visit (p-> data); <br/> r = P; <br/> P = NULL; <br/>}< br/> destroystack (s); <br/> Return OK; <br/>}

 

Sequence traversal Binary Tree Algorithm

// Copyright (c) 2009, Alex Zhong. all rights reserved. </P> <p> Status levelordertraverse (bitree T, status (visit *) (telemtype E) <br/>{< br/> initqueue (Q ); <br/> P = T; <br/> If (p) <br/> {<br/> If (! Visit (p-> data) <br/> return error; <br/> enqueue (Q, P-> lchild); <br/> enqueue (Q, p-> rchild); <br/> while (q) <br/>{< br/> dequeue (Q, P); <br/> If (! Visit (p-> data) <br/> return error; <br/> If (p-> lchild) <br/> enqueue (Q, P-> lchild ); <br/> If (p-> rchild) <br/> enqueue (Q, P-> rchild ); <br/>}< br/> Return OK; <br/>}

 

Welcome to discussion, criticism, and correction!

Alex Zhong