240312 k진수에서 소수 개수 구하기

public int solution(int n, int k) {
	int answer = 0;
	int[] digits = convertToBaseKArray(n, k);

	int j;
	for (int i = 0; i < digits.length; i = j) {
		j = i + 1;
		while (j < digits.length && digits[j] != 0)
			j++;

		if (isPrime(convertFromBaseK(digits, i, j)))
			answer++;
	}

	return answer;
}

public int[] convertToBaseKArray(int n, int k) {
	int[] result = new int[32];
	int i = 31;

	while (n > 0) {
		result[i--] = n % k;
		n /= k;
	}

	return result;
}

public long convertFromBaseK(int[] digits, int start, int end) {
	long result = 0;
	long multiplier = 1;

	for (int i = end - 1; i >= start; i--) {
		result += digits[i] * multiplier;
		multiplier *= 10;
	}

	return result;
}

public 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