Get nth biggest product of two arrays

nth-biggest-product.php

<?php

class IteratorsPriorityQueue extends SplPriorityQueue {}

function getNthIterator($n, $s, $nthA, $bList) {
  for ($i=0; $i < $s; $i++) {
    yield $nthA * $bList[$i];
  }
}

function getNextIteratorValue(Iterator $iterator) {
  $iterator->key();
  $current = $iterator->current();
  $iterator->next();

  return $current;
}

function getNthBiggestProductGenerator($aList, $bList) {
  $n = count($aList)*count($bList);
  $aMin = min($n, count($aList));
  $bMin = min($n, count($bList));

  rsort($aList);
  rsort($bList);

  $iteratorsPriorityQueue = new IteratorsPriorityQueue;
  $iteratorsPriorityQueue->setExtractFlags($iteratorsPriorityQueue::EXTR_BOTH);

  for ($i=0; $i < $aMin; $i++) {
    $iteratorsPriorityQueue->insert(
      $nthIterator = getNthIterator($i, $bMin, $aList[$i], $bList),
      getNextIteratorValue($nthIterator)
    );
  }

  for ($i=0; $i < $n; $i++) {
    $iteratorWithPriority = $iteratorsPriorityQueue->extract();
    $iterator = $iteratorWithPriority['data'];
    $priority = $iteratorWithPriority['priority'];

    if($iterator->valid()) {
      $iteratorsPriorityQueue->insert($iterator, getNextIteratorValue($iterator));
    }

    yield $priority;
  }
}

$aList = array(3, 5, 24, 306, 48, 25, 25, 205);
$bList = array(73, 48, 25, 1, 2, 3, 508, 401, 2, 200);

$generator = getNthBiggestProductGenerator($aList, $bList);

$abList1 = [];
foreach ($generator as $value) {
  $abList1[] = $value;
}

// Naive approach
$abList2 = [];
foreach($aList as $aKey => $a) {
  foreach($bList as $bKey => $b) {
    $abList2[] = $a*$b;
  }
}
rsort($abList2);

var_dump($abList1 === $abList2);