How to create a nested array of arbitrary depth in

Question

I am trying to create an array of arrays of arrays etc..., except I don't know how many nested levels deep it needs to be until runtime.

Depending on the input, I might need either int[], int[][], int[][][][][][], or anything else. (For context, I am trying to construct an N-dimensional grid for a cellular automaton, where N is passed as a parameter.)

I don't have any code for you because I have no idea how to go about this; I suspect is not possible at all using just arrays. Any help, or alternative solutions, would be appreciated.

Answer 1

The whole construct of multi-dimensional arrays is just the compiler doing some work for you on a big block of memory (ok as some have commented in java this is multiple blocks of memory). One way to deal with the problem you face is to use nested arraylists at runtime. Another (more performant) way is to just allocate a single-dimensional array of the size you need and do the indexing yourself. You could then hide the indexing code in a method that was passed all the details like an array de-reference.

private int[] doAllocate(int[] dimensions)
{
    int totalElements = dimensions[0];

    for (int i=1; i< dimensions.length; i++)
    {
        totalElements *= dimensions[i];
    }

    int bigOne = new int[totalElements];

    return bigOne;
}

private int deReference(int[] dimensions, int[] indicies, int[] bigOne)
{
    int index = 0;

    // Not sure if this is only valid when the dimensions are all the same.
    for (int i=0; i<dimensions.length; i++)
    {
        index += Math.pow(dimensions[i],i) * indicies[dimensions.length - (i + 1)];
    }

    return bigOne[index];
}