[529. Minesweeper] #leetcode

529_0906.java

class Solution {
  // O(9^n) O(1)
    public char[][] updateBoard(char[][] board, int[] click) {
        int m = board.length;
        int n = board[0].length;
        
        if (click.length < 2) return board;
        int i = click[0];
        int j = click[1];
        
        if (board[i][j] == 'M') {
            board[i][j] = 'X';
            return board;
        }
        
        revealBoard(board, m, n, i, j);
        return board;
    }
    
    private void revealBoard(char[][] board, int m, int n, int i, int j) {
        if (i < 0 || i >= m || j < 0 || j >= n) return;
        if (board[i][j] != 'E') return;
        
        int count = 0;
        for (int bi = -1; bi <= 1; bi++) {
            for (int bj = -1; bj <= 1; bj++) {
                if (bi == 0 && bj == 0) continue;
                count += countMines(board, m, n, i+bi, j+bj);
            }
        }
        
        if (count == 0) {
            board[i][j] = 'B';
            for (int bi = -1; bi <= 1; bi++) {
                for (int bj = -1; bj <= 1; bj++) {
                    if (bi == 0 && bj == 0) continue;
                    revealBoard(board, m, n, i+bi, j+bj);
                }
            }
        } else {
            board[i][j] = Character.forDigit(count, 10);
        }
    }
    
    private int countMines(char[][] board, int m, int n, int i, int j) {
        if (i < 0 || i >= m || j < 0 || j >= n) return 0;
        if (board[i][j] == 'M') return 1;
        return 0;
    }
}