This function takes in two set of arrays, merges them and sort them using the quick sort algorithm. It returns a new array of the merged arrays in ascending order. It has a worst case time complexity of O(nlog(n)) and space complexity of 0(log(n))

SortAndMergeArrayOfStudentAges.php

<?php
function SortAndMergeArrayOfStudentAges($firstArray, $secondArray)
{
   if (gettype($firstArray) != 'array' && gettype($secondArray) != 'array') {
        return [];
    }
    if (gettype($firstArray) == 'array' && gettype($secondArray) != 'array') {
        return quickSort($firstArray);
    }

    if (gettype($firstArray) != 'array' && gettype($secondArray) == 'array') {
        return quickSort($secondArray);
    }
    return quickSort(array_merge($firstArray, $secondArray));
}


function quickSort($array)
{
    quickSortHelper($array, 0, count($array) - 1);
    return $array;
}

function quickSortHelper(&$array, $startIndex, $endIndex)
{  
    if ($startIndex >= $endIndex) {
        return;
    }
    $pivotIndex = $startIndex;
    $leftIndex = $startIndex + 1;
    $rightIndex = $endIndex;
    while ($rightIndex >= $leftIndex) {
        if ($array[$leftIndex] > $array[$pivotIndex] && $array[$rightIndex] < $array[$pivotIndex]) {
            swap($array, $leftIndex, $rightIndex);
        }
        if ($array[$leftIndex] <= $array[$pivotIndex]) {
            $leftIndex += 1;
        }
        if ($array[$rightIndex] >= $array[$pivotIndex]) {
            $rightIndex -= 1;
        }
    }
    swap($array, $pivotIndex, $rightIndex);
    $leftSubArrayIsSmaller = $rightIndex - (1 - $startIndex) < $endIndex - ($rightIndex + 1);
    if ($leftSubArrayIsSmaller) {
        quickSortHelper($array, $startIndex, $rightIndex - 1);
        quickSortHelper($array, $rightIndex + 1, $endIndex);
    } else {
        quickSortHelper($array, $rightIndex + 1, $endIndex);
        quickSortHelper($array, $startIndex, $rightIndex - 1);
    }
}
function swap(&$array, $a, $b)
{
    list($array[$a], $array[$b]) = array($array[$b], $array[$a]);
}
$firstArray = [13,15,19];
$secondArray = [11, 13, 18];
// print_r(mergeStudentAges($firstArray, $secondArray));
print_r(SortAndMergeArrayOfStudentAges($firstArray, $secondArray));

Boss, you are right. 😂

Their is always one thing.....

I have updated the solution to accommodate that now.