[프로그래머스] qr code

class Solution {
    public String solution(int q, int r, String code) {
        String answer = "";
        
        for(int i=0;i<code.length();i++){
            char a = code.charAt(i);
            if (i%q==r) answer+=a;
        }
        
        return answer;
    }
    
}

StringBuilder 디게 많이 쓰네..