from typing import List


def get_shrink_board(
    board: List[List[str]],
    is_flatten: bool
) -> List:
    """
        Get only the building placeholder.
        (Note: In other word, remove the row and column header.)

        Parameters
        ----------
        board: List[List[str]]
            2D array containing all the game detail, including column header, row header and placed buildings.

        is_flatten: bool
            A flag that indicate if the result need to be in flatten into 1d array.

        Returns
        -------
        (Note: there are two possible scenario depending on {is_flatten})

        placeholder_list: List[str]
            A 1D array containing all the placeholder. (When is_flatten = True)

        placeholder_list: List[List[str]]
            A 2D array containing all the placeholder. (When is_flatten = False)
    """

    if is_flatten:
        return [board[r][c] for r in range(1, len(board)) for c in range(1, len(board[r]))]
    else:
        return [[board[r][c] for c in range(1, len(board[r]))] for r in range(1, len(board))]