test.php

function solution($S, $K) {
    // write your code in PHP7.0
    print "$S, $K<br>\n";
    $min = "";
    for($i=0; $i<=strlen($S)-$K-1; $i++) {
        $n = $i+$K;
        $string = substr($S,0,$i).substr($S,$n);
        //print "new string $i $string\n";
        $notation = notation($string);
        $len = strlen($notation);
        if($len<$min || $min=="") {
           $min = $len;
           $min_notation = $notation;
        }
    }
    return $min;
}

function notation($S) {
    $prev = "";
    $cnt = 1;
    $notation = "";
    for($i=0; $i<=strlen($S); $i++) {
        $x = substr($S,$i,1);
        if($x==$prev) {
            $cnt++;
        } else {
            $notation .= $prev;
            if($cnt>1) {
                $notation .= $cnt;
            }
            $cnt = 1;
        }
        $prev = $x;
    }
    return $notation;
}