Aufgabe: http://www.phpgangsta.de/kleine-aufgabe-ein-array-umbauen

Lösung für PHPGangstas Aufgabe

<?php
function en(array $a)
{
    $b = array($a[0]);

    for ($i = 1, $l = count($a); $i < $l; $i++) {
        $j = count($b) - 1;
        $x = explode('-', $b[$j]);

        if ((reset($x) >= end($x) && $a[$i] == end($x) - 1) || (reset($x) <= end($x) && $a[$i] == end($x) + 1)) {
            $b[$j] = reset($x) . '-' . $a[$i];
        } else {
            $b[] = $a[$i];
        }
    }

    return $b;
}

function de(array $a)
{
    $b = array();

    foreach ($a as $i) {
        $x = explode('-', $i);
        $b = array_merge($b, range(reset($x), end($x)));
    }

    return $b;
}


$numbers = array(13,81,80,79,78,79,77,76,19,40,41,42,43,44,45,48);
echo join(',', en($numbers)) . '<br />';

$numbers = array(13,'81-78',79,'77-76',19,'40-45',48);
echo join(',', de($numbers)) . '<br />';