StringBuilder를 이용하여 뒤집는다.
StringBuilder sb = new StringBuilder();
sb.reverse();
int a;
Integer.toString(a, n); //n진수로 변환
Integer.parseInt(a, n);
https://school.programmers.co.kr/learn/courses/30/lessons/68935
class Solution {
public int solution(int n) {
int answer = 0;
String a = Integer.toString(n, 3);
StringBuilder sb = new StringBuilder(a);
sb.reverse();
answer = Integer.parseInt(sb.toString(), 3);
return answer;
}
}