BoxList.php

<?php
/**
 * Box packing (3D bin packing, knapsack problem)
 * @package BoxPacker
 * @author Doug Wright
 */
  namespace DVDoug\BoxPacker;

  /**
   * List of boxes available to put items into, ordered by volume
   * @author Doug Wright
   * @package BoxPacker
   */
  class BoxList extends \SplMinHeap {

    /**
     * Compare elements in order to place them correctly in the heap while sifting up.
     * @see \SplMinHeap::compare()
     */
    public function compare($aBoxA, $aBoxB) {
      if ($aBoxB->getInnerVolume() > $aBoxA->getInnerVolume()) {
        return 1;
      }
      else if ($aBoxB->getInnerVolume() < $aBoxA->getInnerVolume()) {
        return -1;
      }
      else {
        return 0;
      }
    }

  }