Word PHP implements Trie tree (dictionary tree)

The concept of Trie tree (Baidu's explanation): Dictionary tree, also known as word search tree, Trie tree, is a tree structure and a variant of hash tree. Typical applications are for counting, sorting and saving a large number of strings (but not limited to strings), so they are often used by search engine systems for text word frequency statistics. Its advantages are: using the common prefix of strings to reduce query time, minimizing unnecessary string comparisons, and querying efficiency is higher than hash trees.

My understanding is that it is used for string search. Each node only contains one character. For example, if the word "world" is entered, the structure of the tree is:

At this time, the word "worab" is entered, Then the structure of the tree is:

So each node must also have a field is_end to identify whether it is the end word. For example, the user inputs wor and searches for all words starting with wor. Assume that there is a word now that is wor, and the search starts from "w". When "r" is retrieved, it needs to be judged that the is_end of the "r" node is true, and wor is added. Go to the results list and continue searching below.

PHP implementation code:

<?php

class Node{

	public $value;                 // 节点值
	public $is_end = false;        // 是否为结束--是否为某个单词的结束节点
	public $childNode = array();   // 子节点
	
	/* 添加孩子节点--注意：可以不为引用函数，因为PHP对象赋值本身就是引用赋值 */
	public function &addChildNode($value, $is_end = false){
		$node = $this->searchChildNode($value);
		if(empty($node)){
			// 不存在节点，添加为子节点
			$node = new Node();
			$node->value = $value;
			$this->childNode[] = $node;
		}
		$node->is_end = $is_end;
		return $node;
	}

	/* 查询子节点 */
	public function searchChildNode($value){
		foreach ($this->childNode as $k => $v) {
			if($v->value == $value){
				// 存在节点，返回该节点
				return $this->childNode[$k];
			}
		}
		return false;
	}
}



/* 添加字符串 */
function addString(&$head, $str){
	$node = null;
	for ($i=0; $i < strlen($str); $i++) {
		if($str[$i] != &#39; &#39;){
			$is_end = $i != (strlen($str) - 1) ? false : true;
			if($i == 0){
				$node = $head->addChildNode($str[$i], $is_end);
			}else{
				$node = $node->addChildNode($str[$i], $is_end);
			}
		}
	}
}

/* 获取所有字符串--递归 */
function getChildString($node, $str_array = array(), $str = ''){
	if($node->is_end == true){
		$str_array[] = $str;
	}
	if(empty($node->childNode)){
		return $str_array;
	}else{
		foreach ($node->childNode as $k => $v) {
			$str_array = getChildString($v, $str_array, $str . $v->value);
		}
		return $str_array;
	}
}

/* 搜索 */
function searchString($node, $str){
	for ($i=0; $i < strlen($str); $i++) {
		if($str[$i] != &#39; &#39;){
			$node = $node->searchChildNode($str[$i]);
			// print_r($node);
			if(empty($node)){
				// 不存在返回空
				return false;
			}
		}
	}
	return getChildString($node);
}


/* 调用测试开始 */
$head = new Node;   // 树的head

// 添加单词
addString($head, 'hewol');
addString($head, 'hemy');
addString($head, 'heml');
addString($head, 'you');
addString($head, 'yo');

// 获取所有单词
$str_array = getChildString($head);

// 搜索
$search_array = searchString($head, 'hem');
// 循环打印所有搜索结果
foreach ($search_array as $key => $value) {
	echo 'hem' . $value . '<br>';  // 输出带上搜索前缀
}

The above introduces the word PHP implementation of Trie tree (dictionary tree), including the word content, I hope it will be helpful to friends who are interested in PHP tutorials.