프로그래머스 - 자릿수 더하기

https://school.programmers.co.kr/learn/courses/30/lessons/12931

public class Solution {
    public int solution(int n) {
        int answer = 0;
        String s = Integer.toString(n);
        for(int i = 0; i < s.length(); i++){
            answer += Integer.parseInt(s.substring(i, i+1));
        }
        return answer;
    }
}