Creating an array(?) of Sets in Java

Question

I'm trying to write an algorithm that finds the number of solutions in a given partially filled in Sudoku board. i.e. given

"1 6 4 0 0 0 0 0 2",
"2 0 0 4 0 3 9 1 0",
"0 0 5 0 8 0 4 0 7",
"0 9 0 0 0 6 5 0 0",
"5 0 0 1 0 2 0 0 8",
"0 0 8 9 0 0 0 3 0",
"8 0 9 0 4 0 2 0 0",
"0 7 3 5 0 9 0 0 1",
"4 0 0 0 0 0 6 7 9"

where 0s represent blank spots. I want to create 3 separate arrays of sets, one for each set of numbers in each column, row, and 3x3 square. I am trying the declaration:

horizontal = new HashSet<Integer>[9];

Where private HashSet[] horizontal is declared earlier, but this doesn't work. What is the correct declaration or can I not make declare an array of Sets?

possible duplicate of [Java how to: Generic Array creation ](stackoverflow.com/questions/529085/…) — Bert F
– Bert F, Commented Feb 1, 2011 at 23:56

rlibby · Accepted Answer · 2011-02-01 23:55:56Z

2

The problem is the type parameter. You can't create generic arrays in Java. You can remove the type parameter and it will work, but you should get a warning about unchecked operations.

answered Feb 1, 2011 at 23:55

rlibby

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Michael K · Accepted Answer · 2011-02-02 00:29:32Z

1

You might try this:

horizontal = new ArrayList<HashMap<Integer>>();

Access it with horizontal.get(1); and you can treat it the same way as a normal array. As @user599152 said, you can't create generic arrays. So you need to figure out another way. A list is probably your best bet.

answered Feb 2, 2011 at 0:29

Michael K

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jzd · Accepted Answer · 2011-02-02 00:15:11Z

0

An array of sets is a strange way to store the data. A 2d array or a 2d array of 2d arrays might be a much more intuitive way of modeling this. Possibly even a 2d array of some custom class ("SudokuCube") would also work better than an array of sets.

answered Feb 2, 2011 at 0:15

jzd

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