HackerRank::Super Reduced String

<?php
$_fp = fopen("php://stdin", "r");
$str = trim(fgets($_fp));
$str = str_split($str);

function removeAdjacent($s, $len)
{
    $j = 0;

    for ($i = 1; $i < $len; $i++) {
        while (($j >= 0) && $i < $len && $s[$i] == $s[$j]) {
            $i++;
            $j--;
        }

        if ($i < $len) {
            $s[++$j] = $s[$i];
        }
    }

    $uniqChar = [];

    for ($k = 0; $k <= $j; $k++) {
        $uniqChar[$k] = $s[$k];
    }

    return $uniqChar;
}

$str = removeAdjacent($str, count($str));

if (count($str)) {
    echo implode('', $str);    
} else {
    echo 'Empty String';
}