lua-users home
lua-l archive

[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index] [Thread Index]

On 1-Dec-05, at 7:11 PM, Jens Alfke wrote:

Interesting. This really reminds me of the priority queue, a data structure that lets you push in values and very efficiently pop out the "highest priority" (i.e. largest/smallest) value. It's often used in thread schedulers (to pick the highest-priority ready thread) and simulation engines (to process the chronologically next event.)

A priority queue is usually implemented as a heap, which is a partially-ordered complete binary tree*. The lowest value is always at the top of the tree, and it's very efficient (like O(log n)) to remove it, and to add new values to the tree. I think it's essentially the same sort of lazy sort that you're describing.

Not really, although it certainly has points in common. (For a priority queue / heap implementation in Lua, see the code samples at <>)

Both quicksort and heapsort have an implicit binary tree in their implementation. The difference is that quicksort builds its binary tree top-down and heapsort builds the binary tree bottom-up. The practical consequence is that lazy heapsort lets you lazily sort the initial segment of the result vector (although the usual implementation does this destructively) whereas my lazy quicksort lets you lazily sort at any point in the vector. In other words, you could not produce an efficient solution to the income disparity problem by using a lazy heapsort, as far as I can see; you'd need to sort almost the entire vector to do so.