PHP Searching and Sorting Algorithm: Merge sort
PHP Searching and Sorting Algorithm: Exercise-17 with Solution
Write a PHP program to sort a list of elements using Merge sort.
According to Wikipedia "Merge sort (also commonly spelled mergesort) is an O (n log n) comparison-based sorting algorithm. Most implementations produce a stable sort, which means that the implementation preserves the input order of equal elements in the sorted output."
Pictorial presentation - Merge search algorithm :
Sample Solution :
PHP Code :
<?php
function merge_sort($my_array){
if(count($my_array) == 1 ) return $my_array;
$mid = count($my_array) / 2;
$left = array_slice($my_array, 0, $mid);
$right = array_slice($my_array, $mid);
$left = merge_sort($left);
$right = merge_sort($right);
return merge($left, $right);
}
function merge($left, $right){
$res = array();
while (count($left) > 0 && count($right) > 0){
if($left[0] > $right[0]){
$res[] = $right[0];
$right = array_slice($right , 1);
}else{
$res[] = $left[0];
$left = array_slice($left, 1);
}
}
while (count($left) > 0){
$res[] = $left[0];
$left = array_slice($left, 1);
}
while (count($right) > 0){
$res[] = $right[0];
$right = array_slice($right, 1);
}
return $res;
}
$test_array = array(100, 54, 7, 2, 5, 4, 1);
echo "Original Array : ";
echo implode(', ',$test_array );
echo "\nSorted Array :";
echo implode(', ',merge_sort($test_array))."\n";
?>
Sample Output:
Original Array : 100, 54, 7, 2, 5, 4, 1 Sorted Array : 1, 2, 4, 5, 7, 54, 100
Flowchart :
PHP Code Editor:
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PHP: Tips of the Day
How to Sort Multi-dimensional Array by Value?
Try a usort, If you are still on PHP 5.2 or earlier, you'll have to define a sorting function first:
Example:
function sortByOrder($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
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