240814 거울 설치

static final int[][] DIRECTIONS = { { -1, 0 }, { 0, 1 }, { 1, 0 }, { 0, -1 } };

static class Point {
	public final int row;
	public final int col;

	public Point(int row, int col) {
		this.row = row;
		this.col = col;
	}

	public static boolean isValid(int row, int col, int size) {
		return row >= 0 && row < size && col >= 0 && col < size;
	}
}

public static void main(String[] args) throws IOException {
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	int size = Integer.parseInt(br.readLine());

	char[][] map = new char[size][];
	List<Point> targets = new ArrayList<>(2);
	for (int i = 0; i < size; i++) {
		map[i] = br.readLine().toCharArray();
		for (int j = 0; targets.size() < 2 && j < size; j++) {
			if (map[i][j] == '#') {
				targets.add(new Point(i, j));
			}
		}
	}

	int result = bfs(map, targets);
	System.out.println(result);
}

private static int bfs(char[][] map, List<Point> targets) {
	int size = map.length;
	Queue<Point> queue = new ArrayDeque<>();
	boolean[][] visited = new boolean[size][size];

	Point start = targets.get(0);
	Point end = targets.get(1);
	queue.add(start);
	visited[start.row][start.col] = true;

	int depth = 0;

	while (!queue.isEmpty()) {
		int stepSize = queue.size();

		for (int i = 0; i < stepSize; i++) {
			Point current = queue.poll();

			for (int[] direction : DIRECTIONS) {
				int row = current.row;
				int col = current.col;

				while (true) {
					row += direction[0];
					col += direction[1];

					if (!Point.isValid(row, col, size) || map[row][col] == '*')
						break;

					if (row == end.row && col == end.col)
						return depth;

					if (!visited[row][col]) {
						visited[row][col] = true;
						if (map[row][col] == '!') {
							queue.add(new Point(row, col));
						}
					}
				}
			}
		}

		depth++;
	}

	return Integer.MAX_VALUE;
}

출처:https://www.acmicpc.net/problem/2151