High-speed retrieval algorithm and its application in PHP

As a popular server-side programming language, PHP plays an indispensable role in Web application development. In actual development, we often need to perform operations such as retrieval and search on large amounts of data. At this time, high-speed retrieval algorithms have become a very important direction.

This article will introduce high-speed retrieval algorithms commonly used in PHP and their applications.

1. Overview

In the data structure, retrieval refers to finding data records with specified conditions in the data collection. Common retrieval methods include linear search, binary search, hash search, etc.

Linear search is the most basic search algorithm. It traverses all elements in the data collection in turn and matches the target data one by one until the target data is found. The time complexity is O(n).

Binary search is a more efficient search algorithm. It uses the characteristics of ordered sequences to reduce the search range by half each time and quickly lock the location of the target data. The time complexity is O(log2n) and the efficiency is very high.

Hash search is a high-speed search algorithm based on a hash table. It can quickly locate the location of the target data in the hash table. The time complexity is O(1). It is a very efficient method. algorithm.

In PHP, some commonly used high-speed search algorithms include ordered array search, binary search, hash search, Trie tree search, etc.

2. Ordered array search

Ordered array search is a search algorithm based on ordered arrays. It takes advantage of the orderly arrangement of array elements. Each search can quickly narrow down the search. scope.

In PHP, ordered array search can be implemented through PHP's built-in array_search() function. This function is implemented using a binary search algorithm and can quickly locate the position of the target data in the array. For example, to find element 10 in an array containing 100000 ordered elements, the code is as follows:

$arr ​​= range(1, 100000); // Generate an ordered array of 100000 elements
$index = array_search(10, $arr); // Find the position of target element 10 in the array

Since the array_search() function is a standard library function that comes with PHP, its performance is very efficient and time is complex The degree is O(log2n).

3. Binary search

Binary search is a divide-and-conquer algorithm based on an ordered array. It divides the array into two equal parts and determines whether the target data is in the left half or The right half, and continue to recursively search for target data to quickly achieve data retrieval.

In PHP, binary search can be implemented through custom functions. For example, to find element 20 in an array containing 100,000 ordered elements, the code is as follows:

function binary_search($arr, $low, $high, $target) {

while ($low <= $high) {
    $mid = ($low + $high) >> 1;
    if ($arr[$mid] === $target) {
        return $mid;
    } elseif ($arr[$mid] > $target) {
        $high = $mid - 1;
    } else {
        $low = $mid + 1;
    }
}

return -1;

}

$arr ​​= range(1, 100000); // Generate an ordered array of 100000 elements
$index = binary_search($arr, 0, 99999, 20); // Find the target The position of element 20 in the array

Since the time complexity of the binary search algorithm is O(log2n), it is very efficient and suitable for retrieval of large amounts of data.

4. Hash search

Hash search is a high-speed search algorithm based on a hash table. It can be implemented in PHP through PHP's built-in hash() function.

First, we need to insert data into the hash table. We can traverse the array through a foreach loop, use the value of each element as the key, and insert the index of the element into the hash table as the value. For example:

$arr ​​= range(1, 100000); // Generate an array of 100000 elements
$hash = array();

foreach ($arr as $k = > $v) {

$hash[$v] = $k; // 插入元素到哈希表中

}

Then, we can retrieve the target element through the hash() function. For example, in the above example, the code to retrieve element 20 is as follows:

$index = isset($hash[20]) ? $hash[20] : -1; // Retrieve element 20 in the array Position in

Since the time complexity of the hash search algorithm is O(1), it is very efficient and suitable for retrieval of large-scale data.

5. Trie tree search

Trie tree is an efficient string retrieval algorithm based on tree structure, which can achieve fast string matching and prefix search. In PHP, this can be achieved by customizing the Trie tree class.

First, we need to build a Trie tree and insert the string into the Trie tree. For example, in the following code, the three strings "hello", "world" and "php" are inserted into the Trie tree:

class Trie {

private $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->is_end = true;
}

}

class TrieNode {

public $children = array();
public $is_end = false;

}

$trie = new Trie();
$trie->insert("hello");
$trie-> ;insert("world");
$trie->insert("php");

Then, we can find the target string through the Trie tree. For example, in the above example, the code to find the string "php" would look like this:

function search($trie, $word) {

$node = $trie->root;

for ($i = 0; $i < strlen($word); $i++) {
    $char = $word{$i};

    if (!isset($node->children[$char])) {
        return false;
    }

    $node = $node->children[$char];
}

return $node->is_end;

}

$found = search($trie, "php"); // Search for the string "php"

Since the time complexity of the Trie tree is related to the length of the string, the Trie tree is suitable for scenarios where the string length is fixed. Such as keyword filtering, string matching and other scenarios.

6. Summary

This article introduces commonly used high-speed retrieval algorithms and their applications in PHP, including ordered array search, binary search, hash search, Trie tree search, etc.

These algorithms each have their own advantages and disadvantages, and can be used in different scenarios to achieve efficient data retrieval and string matching. In actual development, we need to choose the appropriate algorithm based on the specific situation.

The above is the detailed content of High-speed retrieval algorithm and its application in PHP. For more information, please follow other related articles on the PHP Chinese website!