Given the subject of the original, I have no doubt that he doesn't need to fully populate the array, but is instead representing a sparse solution space based on a set of input data. Fully representing the array is not necessary in this case, you just have to be able to store data at any of the arbitrarily indexed locations and fetch it back later, along with potential default values for locations that are read from before being stored to.

The problem's less of an issue than it might seem--more than anything else the limiting factor is the number of real elements stored, not the potential number of places data could be stored into.