The underlying principle of finding specific elements in PHP arrays

PHP Array search element principle: determine the hash value of the key. Find the bucket corresponding to the hash value. Iterate over and compare key-value pairs within the bucket. Returns the element when a matching key is found.

The underlying principle of PHP array to find specific elements

In PHP, an array is an ordered data structure, in which Elements are stored as key-value pairs. In order to find a specific element, the following steps are performed under the hood:

1. Determine the hash value:When the array key is a string, PHP calculates its hash value (integer value).
2. Bucket search: The array is divided into multiple "buckets", and each hash value corresponds to a bucket. In the database/hashtable (hash table), the corresponding hash value is calculated according to the key, so that the position in the table can be known. There is also an algorithm for calculating the hash value. The hash value is saved based on the size of the key. The same key The calculated hash value is the same. The hash value can be repeated, so if multiple keys are saved at the same time, with the same key and the same hash value, then collision will occur. At this time, this problem can be solved through the zipper method, open addressing method, etc. .
3. Traverse buckets: In the corresponding bucket, compare with the keys of the target element one by one.
4. Key matching: If a matching key is found, the element is returned.

Actual case:

<?php
$arr = ['name' => 'John', 'age' => 30, 'city' => 'New York'];

// 使用 in_array() 函数（线性搜索）
if (in_array('John', $arr)) {
    echo "John exists in the array.\n";
}

// 使用 array_key_exists() 函数（哈希查找）
if (array_key_exists('age', $arr)) {
    echo "age key exists in the array.\n";
}
?>

Output:

John exists in the array.
age key exists in the array.

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