function printPairsWithSpecificDifference($arr, $difference) {
$size = count($arr);
for ($i = 0; $i < $size; $i++) {
for ($j = $i + 1; $j < $size; $j++)
if ($arr[$i] - $arr[$j] == $difference or $arr[$j] - $arr[$i] == $difference)
echo $arr[$i] . " " . $arr[$j] . "\n";
}
}
$arr = array(25, 16, 8, 12, 20, 17, 0, 4, 21, 26);
$difference = 4;
printPairsWithSpecificDifference($arr, $difference);
/*
run:
25 21
16 12
16 20
8 12
8 4
17 21
0 4
*/