Solution.java

class Solution {
    private char[][] board;
    private int m;
    private int n;

    public char[][] updateBoard(char[][] board, int[] click) {
        m = board.length;
        n = board[0].length;
        this.board = board;
        int i = click[0], j = click[1];
        if (board[i][j] == 'M') {
            board[i][j] = 'X';
        } else {
            dfs(i, j);
        }
        return board;
    }

    private void dfs(int i, int j) {
        int cnt = 0;
        for (int x = i - 1; x <= i + 1; ++x) {
            for (int y = j - 1; y <= j + 1; ++y) {
                if (x >= 0 && x < m && y >= 0 && y < n && board[x][y] == 'M') {
                    ++cnt;
                }
            }
        }
        if (cnt > 0) {
            board[i][j] = (char) (cnt + '0');
        } else {
            board[i][j] = 'B';
            for (int x = i - 1; x <= i + 1; ++x) {
                for (int y = j - 1; y <= j + 1; ++y) {
                    if (x >= 0 && x < m && y >= 0 && y < n && board[x][y] == 'E') {
                        dfs(x, y);
                    }
                }
            }
        }
    }
}