231122 교점에 별 만들기

public String[] solution(int[][] line) {
	List<long[]> intersections = findIntersections(line);
	long minX = Long.MAX_VALUE;
	long maxX = Long.MIN_VALUE;
	long minY = Long.MAX_VALUE;
	long maxY = Long.MIN_VALUE;

	for (long[] intersection : intersections) {
		long x = intersection[0];
		long y = intersection[1];
		minX = Math.min(minX, x);
		maxX = Math.max(maxX, x);
		minY = Math.min(minY, y);
		maxY = Math.max(maxY, y);
	}

	boolean[][] answerTemp = moveAnswer(intersections, minX, maxX, minY, maxY);

	return makeAnswer(answerTemp);
}

private List<long[]> findIntersections(int[][] line) {
	List<long[]> intersections = new ArrayList<>();

	for (int i = 0; i < line.length; i++) {
		long a = line[i][0];
		long b = line[i][1];
		long e = line[i][2];

		for (int j = i + 1; j < line.length; j++) {
			long c = line[j][0];
			long d = line[j][1];
			long f = line[j][2];
			long xDown = a * d - b * c;

			if (xDown == 0) {
				continue;
			}

			double x = (b * f - e * d) / (double) xDown;
			double y = (e * c - a * f) / (double) xDown;

			if (x == Math.ceil(x) && y == Math.ceil(y)) {
				long xLong = (long) x;
				long yLong = (long) y;
				intersections.add(new long[] { xLong, yLong });
			}
		}
	}

	return intersections;
}

private boolean[][] moveAnswer(List<long[]> intersections, long minX, long maxX, long minY, long maxY) {
	boolean[][] answerTemp = new boolean[(int) (maxY - minY + 1)][(int) (maxX - minX + 1)];

	for (long[] intersection : intersections) {
		int x = (int) (intersection[0] - minX);
		int y = (int) (maxY - intersection[1]);
		answerTemp[y][x] = true;
	}

	return answerTemp;
}

private String[] makeAnswer(boolean[][] answerTemp) {
	String[] answer = new String[answerTemp.length];

	for (int i = 0; i < answer.length; i++) {
		StringBuilder sb = new StringBuilder();
		for (boolean b : answerTemp[i]) {
			sb.append(b ? "*" : ".");
		}
		answer[i] = sb.toString();
	}

	return answer;
}

출처:https://school.programmers.co.kr/learn/courses/30/lessons/87377