func countBattleships(board [][]byte) (cnt int) {
	m := len(board)
	if m == 0 {
		return
	}
	n := len(board[0])
	if n == 0 {
		return
	}
	for i := 0; i < m; i++ {
		for j := 0; j < n; j++ {
			if board[i][j] == 'X' {
				fill(board, j, i, m, n)
				cnt++
				j++
			}
		}
	}
	return
}

func fill(board [][]byte, x, y, m, n int) {
	board[y][x] = '.'
	for i := x + 1; i < n && board[y][i] == 'X'; i++ {
		board[y][i] = '.'
	}
	for i := y + 1; i < m && board[i][x] == 'X'; i++ {
		board[i][x] = '.'
	}
}