240720 백조의 호수

static int[] dx = {-1, 1, 0, 0};
static int[] dy = {0, 0, -1, 1};
static int rows;
static int cols;
static char[][] board;
static boolean[][] visitedSwan;
static boolean[][] visitedWater;
static ArrayDeque<Place> swanQueue = new ArrayDeque<>();
static ArrayDeque<Place> waterQueue = new ArrayDeque<>();
static Place swanEnd;

public static void main(String[] args) throws IOException {
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	StringTokenizer st = new StringTokenizer(br.readLine());
	
	rows = Integer.parseInt(st.nextToken());
	cols = Integer.parseInt(st.nextToken());
	
	visitedSwan = new boolean[rows][cols];
	visitedWater = new boolean[rows][cols];
	board = new char[rows][cols];

	initializeQueues(br);

	int days = 0;
	while (!swanFound()) {
		meltIce();
		days++;
	}
	System.out.println(days);
}

private static void initializeQueues(BufferedReader br) throws IOException {
	for (int i = 0; i < rows; i++) {
		board[i] = br.readLine().toCharArray();
		for (int j = 0; j < cols; j++) {
			if (board[i][j] == 'L') {
				board[i][j] = '.';
				if (swanQueue.isEmpty()) {
					swanQueue.add(new Place(i, j));
					visitedSwan[i][j] = true;
				} else {
					swanEnd = new Place(i, j);
				}
			}
			if (board[i][j] == '.') {
				waterQueue.add(new Place(i, j));
				visitedWater[i][j] = true;
			}
		}
	}
}

private static boolean swanFound() {
	swanQueue = bfs(swanQueue, visitedSwan, false);
	return visitedSwan[swanEnd.x][swanEnd.y];
}

private static void meltIce() {
	waterQueue = bfs(waterQueue, visitedWater, true);
}

private static ArrayDeque<Place> bfs(ArrayDeque<Place> queue, boolean[][] visited, boolean melt) {
	ArrayDeque<Place> newQueue = new ArrayDeque<>();
	while (!queue.isEmpty()) {
		Place current = queue.poll();
		for (int i = 0; i < 4; i++) {
			int nx = current.x + dx[i];
			int ny = current.y + dy[i];
			if (isValid(nx, ny) && !visited[nx][ny]) {
				visited[nx][ny] = true;
				if (board[nx][ny] == 'X') {
					newQueue.add(new Place(nx, ny));
					if (melt) board[nx][ny] = '.';
				} else {
					queue.add(new Place(nx, ny));
				}
			}
		}
	}
	return newQueue;
}

private static boolean isValid(int x, int y) {
	return x >= 0 && x < rows && y >= 0 && y < cols;
}

static class Place {
	int x;
	int y;
	Place(int x, int y) {
		this.x = x;
		this.y = y;
	}
}

출처:https://www.acmicpc.net/problem/3197