Backend Development
PHP Tutorial
PHP implements pre-order, in-order and post-order traversal binary tree operation examples
PHP implements pre-order, in-order and post-order traversal binary tree operation examples
This article mainly introduces PHP to implement pre-order, in-order and post-order traversal operations on binary trees based on non-recursive algorithms. It analyzes the principles of PHP using non-recursive algorithms to perform pre-order, in-order and post-order traversal operations on binary trees based on examples. Friends who need it can refer to the specific implementation techniques. I hope it can help everyone.
Overview:
The principle of binary tree traversal is as follows:
For the binary tree traversal shown in the above figure:
1. Preorder traversal: traverse the root node first, then traverse the left subtree, and finally traverse the right subtree.
ABDHECFG
2. In-order traversal: first traverse the left subtree, then traverse the root node, and finally traverse the right subtree.
HDBEAFCG
3. Post-order traversal: first traverse the left subtree, then traverse the right subtree, and finally traverse the root node.
HDEBFGCA
Implementation method:
Pre-order traversal: Using the first-in-last-out feature of the stack, first visit the root node, then push the right subtree, and then push left subtree. When taking it out in this way, the left subtree is taken out first, and the right subtree is taken out last.
function preorder($root){
$stack = array();
array_push($stack, $root);
while(!empty($stack)){
$center_node = array_pop($stack);
echo $center_node->value; // 根节点
if($center_node->right != null)
array_push($stack, $center_node->right); // 压入右子树
if($center_node->left != null)
array_push($stack, $center_node->left); // 压入左子树
}
}In-order: It needs to be traversed from bottom to top, so first push the left subtree onto the stack, and then access the root nodes and nodes one by one Right subtree.
function inorder($root){
$stack = array();
$center_node = $root;
while(!empty($stack) || $center_node != null){
while($center_node != null){
array_push($stack, $center_node);
$center_node = $center_node->left;
}
$center_node = array_pop($stack);
echo $center_node->value;
$center_node = $center_node->right;
}
}Post-order: first store the root node, then store the left subtree and right subtree in sequence. Then output.
function tailorder($root){
$stack = array();
$outstack = array();
array_push($$stack, $root);
while($empty($stack)){
$center_node = array_pop($stack);
array_push($outstack, $center_node);
if($center_node->right != null)
array_push($stack, $center_node->right);
if($center_node->left != null)
array_push($stack, $center_node->left);
}
while($empty($outstack)){
$center_node = array_pop($outstack);
echo $center_node->value;
}
}Related recommendations:
How to use PHP to determine whether a binary tree is symmetrical
JavaScript to implement a binary tree Pre-order, in-order and post-order traversal methods
Detailed explanation of the binary tree traversal algorithm sample code implemented in PHP
The above is the detailed content of PHP implements pre-order, in-order and post-order traversal binary tree operation examples. For more information, please follow other related articles on the PHP Chinese website!
Hot AI Tools
Undresser.AI Undress
AI-powered app for creating realistic nude photos
AI Clothes Remover
Online AI tool for removing clothes from photos.
Undress AI Tool
Undress images for free
Clothoff.io
AI clothes remover
Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!
Hot Article
Hot Tools
Notepad++7.3.1
Easy-to-use and free code editor
SublimeText3 Chinese version
Chinese version, very easy to use
Zend Studio 13.0.1
Powerful PHP integrated development environment
Dreamweaver CS6
Visual web development tools
SublimeText3 Mac version
God-level code editing software (SublimeText3)
Hot Topics
PHP 8.4 Installation and Upgrade guide for Ubuntu and Debian
Dec 24, 2024 pm 04:42 PM
PHP 8.4 brings several new features, security improvements, and performance improvements with healthy amounts of feature deprecations and removals. This guide explains how to install PHP 8.4 or upgrade to PHP 8.4 on Ubuntu, Debian, or their derivati
7 PHP Functions I Regret I Didn't Know Before
Nov 13, 2024 am 09:42 AM
If you are an experienced PHP developer, you might have the feeling that you’ve been there and done that already.You have developed a significant number of applications, debugged millions of lines of code, and tweaked a bunch of scripts to achieve op
How To Set Up Visual Studio Code (VS Code) for PHP Development
Dec 20, 2024 am 11:31 AM
Visual Studio Code, also known as VS Code, is a free source code editor — or integrated development environment (IDE) — available for all major operating systems. With a large collection of extensions for many programming languages, VS Code can be c
Explain JSON Web Tokens (JWT) and their use case in PHP APIs.
Apr 05, 2025 am 12:04 AM
JWT is an open standard based on JSON, used to securely transmit information between parties, mainly for identity authentication and information exchange. 1. JWT consists of three parts: Header, Payload and Signature. 2. The working principle of JWT includes three steps: generating JWT, verifying JWT and parsing Payload. 3. When using JWT for authentication in PHP, JWT can be generated and verified, and user role and permission information can be included in advanced usage. 4. Common errors include signature verification failure, token expiration, and payload oversized. Debugging skills include using debugging tools and logging. 5. Performance optimization and best practices include using appropriate signature algorithms, setting validity periods reasonably,
PHP Program to Count Vowels in a String
Feb 07, 2025 pm 12:12 PM
A string is a sequence of characters, including letters, numbers, and symbols. This tutorial will learn how to calculate the number of vowels in a given string in PHP using different methods. The vowels in English are a, e, i, o, u, and they can be uppercase or lowercase. What is a vowel? Vowels are alphabetic characters that represent a specific pronunciation. There are five vowels in English, including uppercase and lowercase: a, e, i, o, u Example 1 Input: String = "Tutorialspoint" Output: 6 explain The vowels in the string "Tutorialspoint" are u, o, i, a, o, i. There are 6 yuan in total
How do you parse and process HTML/XML in PHP?
Feb 07, 2025 am 11:57 AM
This tutorial demonstrates how to efficiently process XML documents using PHP. XML (eXtensible Markup Language) is a versatile text-based markup language designed for both human readability and machine parsing. It's commonly used for data storage an
Explain late static binding in PHP (static::).
Apr 03, 2025 am 12:04 AM
Static binding (static::) implements late static binding (LSB) in PHP, allowing calling classes to be referenced in static contexts rather than defining classes. 1) The parsing process is performed at runtime, 2) Look up the call class in the inheritance relationship, 3) It may bring performance overhead.
What are PHP magic methods (__construct, __destruct, __call, __get, __set, etc.) and provide use cases?
Apr 03, 2025 am 12:03 AM
What are the magic methods of PHP? PHP's magic methods include: 1.\_\_construct, used to initialize objects; 2.\_\_destruct, used to clean up resources; 3.\_\_call, handle non-existent method calls; 4.\_\_get, implement dynamic attribute access; 5.\_\_set, implement dynamic attribute settings. These methods are automatically called in certain situations, improving code flexibility and efficiency.
