Longest Substring Without Repeating Characters – Sliding Window

class Solution {
/**
 * @param String $s
 * @return Integer
 */
function lengthOfLongestSubstring($s) {
    $len = strlen($s);
    $max = 0;
    $tempMax = 0;
    $freq = array();

    #loop through array
    for($i = 0; $i < $len; $i++){


        #if IN character in freq array
        if(array_key_exists($s[$i], $freq)) {
            var_dump( $s[$i]);
            $max = max($max, $tempMax);
            $tempMax = 0;
            $this->resetFreq($freq);
        }
        else {
            #if not in freq array
            $freq[$s[$i]] = 1;
            $tempMax +=1 ;
        }

   }
    return $max;
}
public function resetFreq(array $freq) : array {

    return array();
}
}