5.17: Making a Move by Updating the Board Data Structure

def makeMove(board, move):
    # This function does not check if the move is valid.
    blankx, blanky = getBlankPosition(board)

    if move == UP:
        board[blankx][blanky], board[blankx][blanky + 1] = board[blankx][blanky + 1], board[blankx][blanky]
    elif move == DOWN:
        board[blankx][blanky], board[blankx][blanky - 1] = board[blankx][blanky - 1], board[blankx][blanky]
    elif move == LEFT:
        board[blankx][blanky], board[blankx + 1][blanky] = board[blankx + 1][blanky], board[blankx][blanky]
    elif move == RIGHT:
        board[blankx][blanky], board[blankx - 1][blanky] = board[blankx - 1][blanky], board[blankx][blanky]

The data structure in the board parameter is a 2D list that represents where all the tiles are. Whenever the player makes a move, the program needs to update this data structure. What happens is that the value for the tile is swapped with the value for the blank space.

The makeMove() function doesn’t have to return any values, because the board parameter has a list reference passed for its argument. This means that any changes we make to board in this function will be made to the list value that was passed to makeMove(). (You can review the concept of references at http://invpy.com/references.)

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