[Programmers]3진법 뒤집기(난이도:★★★★)

https://programmers.co.kr/learn/courses/30/lessons/68935

코딩테스트 연습 - 3진법 뒤집기

class Solution {
    public int solution(int n) {
        long a = change((long)n);
        a = reverseNumber(a);
        int answer = changeTen(a);
        return answer;
    }
    // 3진법 - > 10진법
    public int changeTen(long num) {
		 long tmp = num;
		 int idx = 1;
		 int res = 0;
		 while(tmp > 0) {
			 long s = (int) (tmp % 10L) ;
			 s = s * idx;
			 res += s;
			 idx *= 3;
			 tmp /= 10L;
		 }
		 return res;
	 }
     // 10진법 -> 3진법
	 public long change(long n){
	        long cul = n;
	        long res = 0L;
	        long dis = 1L;
	    
	        while(cul > 0){
	            long tmp = (cul % 3L) * dis;   
	        
	            dis *= 10L;
	            cul = cul / 3L;
	            res += tmp;
	        }
	        return res;
	    }
        // 숫자 뒤집기
	 public long reverseNumber(long num) {
		 long tmp = num;
		 long res = 0L;
		 long count = Long.toString(num).length();
		 long idx = (long)Math.pow(10, count-1L);
		 while(tmp > 0) {
			 long s = (tmp % 10L);
			 res += (s * idx);
			 idx /= 10L;
			 tmp /= 10L;
		 }
		 return res;
	 }
}