hackerrank stringSimilarity solution php

stringSimilarity.php

<?php 

function stringSimilarity( $a) {
        $a = trim($a);
        $cutPrefix = $sum = 0;           
        $length = strlen($a);
        do{            
            $count = 0;
            while($a[$count] === substr($a,$cutPrefix+($count++), 1)){}           
            $sum += $count -1;
        }while($cutPrefix++ < $length);
                  
    return $sum - 1;
}