Question

Here’s a description of the data structure:

It operates like a regular map with get, put, and remove methods, but has a sort method that can be called to sorts the map. However, the map remembers its sorted structure, so subsequent calls to sort can be much quicker (if the structure doesn’t change too much between calls to sort).

For example:

• I call the put method 1,000,000 times.
• I call the sort method.
• I call the put method 100 more times.
• I call the sort method.

The second time I call the sort method should be a much quicker operation, as the map’s structure hasn’t changed much. Note that the map doesn’t have to maintain sorted order between calls to sort.

I understand that it might not be possible, but I’m hoping for O(1) get, put, and remove operations. Something like TreeMap provides guaranteed O(log(n)) time cost for these operations, but always maintains a sorted order (no sort method).

So what’s the design of this data structure?

Edit 1 – returning the top-K entries

Alhough I’d enjoy hearing the answer to the general case above, my use case has gotten more specific: I don’t need the whole thing sorted; just the top K elements.

Data structure for efficiently returning the top-K entries of a hash table (map, dictionary)

Thanks!

Answer 1

Why exactly do you need a sort() function ?
What do you perhaps want and need is a Red-Black Tree.

http://en.wikipedia.org/wiki/Red-black_tree

These trees are automatically sorting your input by a comparator you give. They are complex, but have excellent O(n) characteristics. Couple your tree entries as key with a hash
map as dictionary and you get your datastructure.

In Java it is implemented as TreeMap as instance of SortedMap.