Understand the principles and application scenarios of the Trie tree algorithm in PHP.

Understand the principles and application scenarios of the Trie tree algorithm in PHP

Overview:
Trie tree, also known as dictionary tree or prefix tree, is a multi- Fork tree structure. It is mainly used to solve fast search, insertion and deletion operations of strings. It is an efficient data structure. The core idea of ​​the Trie tree is to use the common prefixes of strings to reduce ineffective searches.

Principle:
The basic structure of a Trie tree is a root node and several sub-nodes, each node represents a character. Starting from the root node, find the corresponding child nodes according to character order until the end of the string. In a Trie tree, the number of child nodes of each node is not fixed and depends on the number of child nodes of the current node. Each node stores a character and pointers to its child nodes.

Specific code implementation:

class TrieNode {
    public $children;
    public $isEndOfWord;
    
    public function __construct() {
        $this->children = array();
        $this->isEndOfWord = false;
    }
}

class Trie {
    public $root;
    
    public function __construct() {
        $this->root = new TrieNode();
    }
    
    public function insert($word) {
        $node = $this->root;
        
        for ($i = 0; $i < strlen($word); $i++) {
            $char = $word[$i];
            
            if (!isset($node->children[$char])) {
                $node->children[$char] = new TrieNode();
            }
            
            $node = $node->children[$char];
        }
        
        $node->isEndOfWord = true;
    }
    
    public function search($word) {
        $node = $this->root;
        
        for ($i = 0; $i < strlen($word); $i++) {
            $char = $word[$i];
            
            if (!isset($node->children[$char])) {
                return false;
            }
            
            $node = $node->children[$char];
        }
        
        return $node->isEndOfWord;
    }
}

Application scenario:

1. Word search: Trie tree can be used to efficiently find whether a word exists in a dictionary. We can insert a word from the dictionary into the Trie tree, and then determine whether the word exists through query operations.
2. String matching: Trie tree can be used to quickly search for all strings that start with a certain string or contain a certain substring. We can insert the string in the text into the Trie tree, and then traverse the Trie tree to find matching strings.
3. Auto-completion: Trie tree can be used to implement the automatic completion function. When the user enters a prefix in the search box, we can find all the strings starting with the prefix by traversing the Trie tree and display them to the user for selection.

Summary:
Trie tree is a relatively efficient data structure for string search, insertion and deletion, suitable for various scenarios. By understanding the principles and applications of Trie trees, we can better use it to solve related problems.

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