Facebook

<?php

$input_data = array();
$i = 0;

while (($line = fgets(STDIN)) !== false) {
  $input_data[$i] = explode(" ", $line);
  $i++;
}

$k = $input_data[0][1];
$numbers = $input_data[1];

$hashMap = array();
$pairs = 0;

foreach ($numbers as $number) {
  $upper_difference = $number + $k;
	$lower_difference = $number - $k;
	if ($hashMap[$upper_difference] == 1) {
		$pairs++;
	}
	if ($hashMap[$lower_difference] == 1) {
	  $pairs++;
	}
	$hashMap[$number] = 1;
}

echo $pairs;

?>