230620 k진수에서 소수 개수 구하기

public static int solution(int n, int k) {
	int answer = 0;
	String s = convertToBaseK(n, k);
	int j;
	for (int i = 0; i < s.length(); i = j) {
		j = i + 1;
		while (j < s.length() && s.charAt(j) != '0')
			j++;

		if (isPrime(Long.parseLong(s.substring(i, j))))
			answer++;
	}

	return answer;
}

public static String convertToBaseK(int n, int k) {
	StringBuilder result = new StringBuilder();

	while (n > 0) {
		result.insert(0, n % k);
		n /= k;
	}

	return result.toString();
}

public static boolean isPrime(long n) {
	if (n <= 1) {
		return false;
	} else if (n == 2) {
		return true;
	}

	for (int i = 2; i <= Math.sqrt(n); i++) {
		if (n % i == 0) {
			return false;
		}
	}

	return true;
}

출처:https://school.programmers.co.kr/learn/courses/30/lessons/92335