StringTokenizer rTokenizer = new StringTokenizer(str,"R",TRUE);
List<String> rTokens = new List<String>();
List<String> result = newList<String>();

while(rTokenizer.hasMoreTokens() {
    rTokens.add(rTokenizer.nextToken());
}

for(String str: rTokens) {
    StringTokenizer kTokenizer = new StringTokenizer(str,"K",TRUE);
    while(kTokenizer.hasMoreTokens() {
        result.add(kTokenizer.nextToken());
    }
}

return result;