CareerCup min range

index.php

<?php
/**
 * CareerCup min range.
 *
 * This is NOT a working solution. By dumb luck it happened to solve the problem
 * for the example lists, but completely crumbles when presented with:
 *     - more than 3 lists.
 *     - sadistic lists like:
 *           array(0, 1, 2, 3, 4)
 *           array(5, 6, 7, 8, 9)
 *           array(10, 11, 12, 13, 14)
 *
 * @link http://www.careercup.com/question?id=16759664
 */

require_once 'item.php';
require_once 'range.php';

// Define lists
$list1 = array(4, 10, 15, 24, 26);
$list2 = array(0, 9, 12, 20);
$list3 = array(5, 18, 22, 30);
$k = 3; // number of lists

// Arange list items into a merged array
$items = array();
for ($i = 1; $i <= $k; $i++) {
    $listName = 'list' . $i;
    foreach ($$listName as $listItem) {
        $items[] = new item($i, $listItem);
    }
}

// Sort merged array by values
usort($items, array('item', 'compare_items'));

// Find the smallest range
$minRange = null;
for ($i = 0; $i < count($items) - 2; $i++) {
    $curRange = new range($items[$i], $items[$i+2]);

    // Skip if both items come from the same list
    if ($curRange->itemMax->list == $curRange->itemMin->list) {
        continue;
    }

    // Skip if current range is larger than existing minimum range, or
    // if the item between the current two is not in the third list
    if (!is_null($minRange)
        && ($minRange->amount() < $curRange->amount()
            || $items[$i+1]->list == $curRange->itemMax->list
            || $items[$i+1]->list == $curRange->itemMin->list)
    ) {
        continue;
    }

    // Current range is value, and smaller than the existing minimum range
    $minRange = $curRange;
}

print_r($minRange->values());

item.php

<?php

class item
{
    public $list;
    public $value;

    public function __construct($list, $value)
    {
        $this->list = $list;
        $this->value = $value;
    }

    public static function compare_items(item $a, item $b)
    {
        if ($a->value == $b->value) {
            return 0;
        }
        return ($a->value < $b->value) ? -1 : 1;
    }
}

range.php

<?php

class range
{
    public $itemMin;
    public $itemMax;

    public function __construct(item $itemMin, item $itemMax)
    {
        $this->itemMin = $itemMin;
        $this->itemMax = $itemMax;
    }

    public function amount()
    {
        return $this->itemMax->value - $this->itemMin->value;
    }

    public function values()
    {
        return array($this->itemMin->value, $this->itemMax->value);
    }
}