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  4. Security Involution
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Security Involution

  • dawn2dusk
     + 0 comments

    php solution because why not...

    $_fp = fopen("php://stdin", "r");

$n = fgets($_fp);
$set = explode(' ', fgets($_fp));
$set = array_combine(range(1, count($set)), $set);
$involution = true;

foreach ($set as $k => $v) {
    if ($k !== intval($set[$v])) {
        $involution = false;
        break;
    }
}

echo ($involution ? "YES" : "NO") . PHP_EOL;