ini_set("memory_limit", "200M");
$a = $b = $c = [];
for($i=0; $i < 1000000; $i++) {
$a[$i] = 1;
}
echo count($a), " ", round(memory_get_usage() / 1024 / 1024), "\n";
foreach(range(500000, 1500000) as $i) {
$b[$i] = 1;
}
echo count($a), " ", round(memory_get_usage() / 1024 / 1024), "\n";
#foreach ($a as $i => $t) { if (isset($b[$i])) $c[] = $b[$i]; }
$c = array_intersect_key($a, $b);
echo count($c), " ", round(memory_get_usage() / 1024 / 1024 ), "\n";
echo count($c), " ", round(memory_get_peak_usage() / 1024 / 1024 ), "\n";