241223 치즈

static class Point {
	int row, col, day;

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

private static final int[] dRow = { 0, 1, 0, -1 };
private static final int[] dCol = { 1, 0, -1, 0 };

public static void main(String[] args) throws IOException {
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	StringTokenizer st = new StringTokenizer(br.readLine());

	int row = Integer.parseInt(st.nextToken());
	int col = Integer.parseInt(st.nextToken());

	boolean[][] isCheese = new boolean[row][col];

	for (int r = 0; r < row; r++) {
		String[] line = br.readLine().split(" ");
		for (int c = 0; c < col; c++) {
			if (line[c].equals("1")) {
				isCheese[r][c] = true;
			}
		}
	}

	int result = meltCheese(row, col, isCheese);
	System.out.println(result);
}

private static int meltCheese(int row, int col, boolean[][] isCheese) {
	Deque<Point> queue = initializeQueue(row, col);
	int[][] contact = new int[row][col];
	boolean[][] visited = new boolean[row][col];

	int days = 0;

	while (!queue.isEmpty()) {
		Point current = queue.poll();

		if (visited[current.row][current.col]) {
			continue;
		}
		visited[current.row][current.col] = true;
		days = current.day;

		for (int dir = 0; dir < 4; dir++) {
			int nextRow = current.row + dRow[dir];
			int nextCol = current.col + dCol[dir];

			if (isOutOfBounds(nextRow, nextCol, row, col) || visited[nextRow][nextCol]) {
				continue;
			}
			if (!isCheese[nextRow][nextCol]) {
				queue.addFirst(new Point(nextRow, nextCol, current.day));
			} else if (++contact[nextRow][nextCol] > 1) {
				queue.addLast(new Point(nextRow, nextCol, current.day + 1));
			}
		}
	}
	return days;
}

private static Deque<Point> initializeQueue(int row, int col) {
	Deque<Point> queue = new ArrayDeque<>();
	for (int c = 0; c < col; c++) {
		queue.add(new Point(0, c, 0));
		queue.add(new Point(row - 1, c, 0));
	}
	for (int r = 1; r < row - 1; r++) {
		queue.add(new Point(r, 0, 0));
		queue.add(new Point(r, col - 1, 0));
	}
	return queue;
}

private static boolean isOutOfBounds(int r, int c, int row, int col) {
	return r < 0 || c < 0 || r >= row || c >= col;
}

출처:https://www.acmicpc.net/problem/2638