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POHow to populate a Java array with variable subarrays?
 

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  1. POHow to populate a Java array with variable subarrays?
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    <p>I'd like to write a Java method that operates something like this:</p> <pre> input 1, output { {0}, {1} } input 2, output { {0, 0}, {0, 1}, {1, 0}, {1, 1} } input 3, output { {0, 0, 0}, {0, 0, 1}, {0, 1, 0}, ... {1, 1, 1} } ... </pre> <p>(I use 0 and 1 in the example for concision; the lowest-level subelements might be HIGH and LOW, 'A' and 'Z', or any two other distinct values.)</p> <p>This feels like a good candidate for recursion, but that's just a feeling at this point. All of my efforts so far have seemed suboptimal.* Any thoughts on a good approach, other than using a different language?</p> <p><sup>* For example: Loop over 0 to (2^input)-1; interpret the number as an [input]-digit binary value; use the binary digits to generate the subarray. Bleah.</sup></p> <p><strong>EDIT: Present generalized iterative solution</strong></p> <pre> public enum Item { ITEM1, ITEM2, ...; // As many as needed private static final int ITEM_COUNT = values().length; public static Item[][] allCombinationsOfSize(int comboSize) { int arraySize = (int) Math.pow(ITEM_COUNT, comboSize); Item array[][] = new Item[arraySize][]; for ( int n = 0 ; n &lt; arraySize ; ++n ) { array[n] = nthSubarray(n, comboSize); } return array; } private static Item[] nthSubarray(int n, int comboSize) { Item combo[] = new Item[comboSize]; for ( int i = comboSize - 1 ; i &gt;= 0 ; --i ) { combo[i] = Item.values()[n % ITEM_COUNT]; n /= ITEM_COUNT; } return combo; } } </pre> <p>I believe that allCombinationsOfSize is the method I'm looking for. I still have a sneaking suspicion that I'm missing something more elegant. Nevertheless, the above allows me to write this in my JUnit test ...</p> <pre> for ( Signal signals[] : Signal.allCombinationsOfSize(pinCount) ) { assertEquals( cls.getSimpleName() + " result", expectedResultFor(cls, signals), actualResultFor(cls, signals) ); } </pre> <p>... which is fairly straightforward.</p>
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    1. COIs this supposed to be homework (real or self-imposed)? Yes, recursion has a natural 'fit', in a couple of different ways. Please note that you're going to want more than one actual method, even if just as helpers (but only one should be exposed). What about using the Collections classes, and possibly dealing with Generics?
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      1. POHow to populate a Java array with variable subarrays?
      1. USClockwork-Muse
    2. COWhy do your current efforts seem suboptimal, and what did you try towards a recursive approach?
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    3. CO@Clockwork-Muse: This isn't homework. I've been messing around with a hardware gate simulator (a personal learning project), and I'm looking to test all possible combinations on pin inputs on a gate. Helper functions are A Good Thing, in my book.
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