LeetCode 130. Surrounded Regions_被围绕的区域

给定一个二维的矩阵，包含 'X' 和 'O'（字母 O）。

找到所有被 'X' 围绕的区域，并将这些区域里所有的 'O' 用 'X' 填充。

示例:

X X X X
X O O X
X X O X
X O X X

运行你的函数后，矩阵变为：

X X X X
X X X X
X X X X
X O X X

解释:

被围绕的区间不会存在于边界上，换句话说，任何边界上的 'O' 都不会被填充为 'X'。 任何不在边界上，或不与边界上的 'O' 相连的 'O' 最终都会被填充为 'X'。如果两个元素在水平或垂直方向相邻，则称它们是“相连”的。

        public void solve(char[][] board) {
		if (board.length <= 0)
			return;
		int rows = board.length;
		int cols = board[0].length;

		for (int i = 0; i < cols; i++) {
			if (board[0][i] == 'O')
				bfs(board, 0, i);
			if (board[rows - 1][i] == 'O')
				bfs(board, rows - 1, i);
		}

		for (int i = 0; i < rows; i++) {
			if (board[i][0] == 'O')
				bfs(board, i, 0);
			if (board[i][cols - 1] == 'O')
				bfs(board, i, cols - 1);
		}

		for (int i = 0; i < rows; i++) {
			for (int j = 0; j < cols; j++) {
				if (board[i][j] == 'O')
					board[i][j] = 'X';
				if (board[i][j] == '+')
					board[i][j] = 'O';
			}
		}
	}

	private void bfs(char[][] board, int i, int j) {
		Integer rows = board.length;
		Integer cols = board[0].length;
		Integer[][] dir = { { 1, 0 }, { 0, 1 }, { -1, 0 }, { 0, -1 } };

		Queue<Integer[]> queue = new LinkedList<Integer[]>();
		board[i][j] = '+';
		queue.offer(new Integer[] { i, j });

		while (!queue.isEmpty() && queue.size() > 0) {
			Integer[] temp = queue.poll();
			for (int k = 0; k < 4; k++) {
				Integer next_i = temp[0] + dir[k][0];
				Integer next_j = temp[1] + dir[k][1];
				if (next_i < 0 || next_i >= rows || next_j < 0 || next_j >= cols || board[next_i][next_j] != 'O')
					continue;
				board[next_i][next_j] = '+';
				queue.offer(new Integer[] { next_i, next_j });
			}
		}
	}