PHP Searching and Sorting Algorithm: Quick sort

Last update on May 30 2022 11:47:43 (UTC/GMT +8 hours)

PHP Searching and Sorting Algorithm: Exercise-1 with Solution

Write a PHP program to sort a list of elements using Quick sort.

Quick sort is a comparison sort, meaning that it can sort items of any type for which a "less-than" relation (formally, a total order) is defined.

Pictorial presentation - Quick Sort algorithm :

Animated visualization of the quicksort algorithm. The horizontal lines are pivot values.

Animation credits : RolandH

Sample Solution:

PHP Code:

<?php
function quick_sort($my_array)
 {
	$loe = $gt = array();
	if(count($my_array) < 2)
	{
		return $my_array;
	}
	$pivot_key = key($my_array);
	$pivot = array_shift($my_array);
	foreach($my_array as $val)
	{
		if($val <= $pivot)
		{
			$loe[] = $val;
		}elseif ($val > $pivot)
		{
			$gt[] = $val;
		}
	}
	return array_merge(quick_sort($loe),array($pivot_key=>$pivot),quick_sort($gt));
}
 
$my_array = array(3, 0, 2, 5, -1, 4, 1);
echo 'Original Array : '.implode(',',$my_array).'\n';
$my_array = quick_sort($my_array);
echo 'Sorted Array : '.implode(',',$my_array);
?>

Sample Output:

Original Array : 3,0,2,5,-1,4,1                             
Sorted Array : -1,0,1,2,3,4,5

Flowchart :

PHP Code Editor:

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Next: Write a PHP program to sort a list of elements using Heap sort.

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PHP: Tips of the Day

How to Sort Multi-dimensional Array by Value?

Try a usort, If you are still on PHP 5.2 or earlier, you'll have to define a sorting function first:

Example:

function sortByOrder($a, $b) {
    return $a['order'] - $b['order'];
}

usort($myArray, 'sortByOrder');

Starting in PHP 5.3, you can use an anonymous function:

usort($myArray, function($a, $b) {
    return $a['order'] - $b['order'];
});

And finally with PHP 7 you can use the spaceship operator:

usort($myArray, function($a, $b) {
    return $a['order'] <=> $b['order'];
});

To extend this to multi-dimensional sorting, reference the second/third sorting elements if the first is zero - best explained below. You can also use this for sorting on sub-elements.

usort($myArray, function($a, $b) {
    $retval = $a['order'] <=> $b['order'];
    if ($retval == 0) {
        $retval = $a['suborder'] <=> $b['suborder'];
        if ($retval == 0) {
            $retval = $a['details']['subsuborder'] <=> $b['details']['subsuborder'];
        }
    }
    return $retval;
});

If you need to retain key associations, use uasort() - see comparison of array sorting functions in the manual

Ref : https://bit.ly/3i77vCC