What are the differences between the shuffled array algorithms of different versions of PHP?

PHP array shuffling algorithm difference: PHP 7.1 and above: Use Fisher-Yates algorithm, uniform distribution, time complexity O(n). Versions below PHP 7: Algorithm using non-uniform distribution, time complexity O(n^2). Optimization suggestion: PHP 7.1 and above use the shuffle() function directly. Versions below PHP 7 use the array_rand() function to generate a random index array and then construct a new array.

Detailed explanation of array shuffling algorithms in different versions of PHP

Array shuffling is very common in practical applications of PHP. Different The PHP version provides different algorithms to achieve this functionality. This article will focus on the differences and optimizations between the array shuffling algorithms of PHP 7.1 and above and PHP 7 and below.

PHP 7.1 and above:

Starting from PHP 7.1, the shuffle() function uses a new Fisher-Yates shuffling algorithm , this algorithm has the following advantages:

• Uniform distribution: This algorithm ensures that each element has an equal chance of appearing anywhere in the array.
• Time complexity is O(n): The running time of this algorithm is proportional to the array size, making it efficient even for large arrays.

Code example:

<?php
$array = [1, 2, 3, 4, 5];
shuffle($array);
print_r($array);

Result:

[3, 5, 2, 1, 4]

PHP 7 and below versions:

PHP 7 and below versions of the shuffle() function uses a different algorithm, which has certain shortcomings. Location:

• Non-uniform distribution: This algorithm does not ensure that each element has an equal chance of appearing anywhere in the array.
• Time complexity is O(n^2): The running time of this algorithm is proportional to the square of the array size, making it inefficient for large arrays.

Code example:

<?php
$array = [1, 2, 3, 4, 5];
shuffle($array);
print_r($array);

Practical case:

Array shuffling is very common in many practical applications Useful, for example:

• Generate random question sets
• Shuffle the order of items in the game
• Create a random playlist

Optimization suggestions:

In order to improve the shuffling performance of large arrays, you can use the following optimization suggestions:

• For PHP 7.1 and above, use the shuffle() function to get good performance.
• For versions below PHP 7, you can use the array_rand() function to generate a random index array and then use that array to build a new array. This approach can improve shuffling performance for large arrays.

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