문자열 다루기 기본

class Solution {
    public boolean solution(String s) {
        boolean answer = true;

        if (s.length() != 4 && s.length() != 6) {
            answer = false;
        } else if (s.length() == 4 || s.length() == 6) {
            for (int i = 0; i < s.length(); i++) {
                char c = s.charAt(i);
                if (!Character.isDigit(c)) {
                    answer = false;
                }
            }
        } else {
            answer = true;
        }
        return answer;
    }
}