The third free response question on the 2016 AP Computer Science exam tasked you with working with a matrix of an arbitrary class. In this case it was a class called Square
. When put into a matrix these Square
reference formed a crossword puzzle.
You were given a shell of the Square
class. When you are given arbitrary classes on an AP exam you will certainly use them in your solutions.
Note that there is no implementation in Square
. They are giving you the constructor signature so that you can create new Square
instances in your code.
Part A – toBeLabeled
The first part of this problem has you implementing a method named toBeLabeled
. toBeLabeled
should return true
if the following two criteria are met.
- The square must be white
- The square does not have a white square immediately above to to the left, or both
We’re given a boolean matrix called blackSquares
that we’ll use to check if a square is black.
To decide if we should label a square the code first looks to see that it’s not black. Since there’s only two options, that means it’s a white square.
Once we know it’s a white square we’ll look and see if it’s in row or column 0. If it is, the square is labeled. If not well look at the row above and column to the left. If either is labeled, then the current square is not labeled.
Part B – Constructor
The constructor should take a boolean matrix identifying black squares and store a matrix of Square
references in the instance variable puzzle
.
First step is to instantiate puzzle
so that it is a 2d array of Square
references. It should be the same size as the blackSquares
parameter. Since this is an AP-A free response we can assume that the matrix is rectangular. All rows will have the same number of columns as row 0.
We also need a variable to keep track of the label number. In the example I call it num
.
Now we iterate through all of the cells using a nest for loop.
If the square is black, we know it won’t be labeled. So we’ll create a new instance of a black square with a label of 0
.
If the square is white we need to check if it should be labeled. Do that by calling the toBeLabeled
method created in Part A. If it should be labeled then create a new Square
instance with a label equal to num
and then increment num
for next time. If it should not be labeled use 0
as the label.
Complete Crossword Class
This is the same code as the examples above, but all together in one file.
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