data structure – humanoid readable

WeakAssQueue

LIFO queue that will drop old elements when needed.

The Idea

Have a Last-In-First-Out queue (implements java.util.Queue<E>) that will release old elements so that garbage collection (GC) can remove them. Like a cache that is a stack.

Stalin-Sort

Stalin-Sort using divide and conquer.

I just love this idea:

I came up with a single pass O(n) sort algorithm I call Stalin-Sort. U iterate down the list of elements checking if they are in order. Any element which is out of order is eliminated. At the end u have a sorted list

But when you have an input such as [42,1,2,3,4,5,6] you just get
[42] instead of [1,2,3,4,5,6]. You can get a better result if you use divide and conquer. And that is something Stalin would do, don’t you think? So I implemented a recursive solution in Java. It tries all possible results, which is not a single pass and therefore defeats the purpose of having a fast O(n) algorithm. And my implementation isn’t even in-place. A new data structure has to be created. That’s why I also added an implementation using a linked list, which is what Mathew describes.

The code is on pastebin: https://pastebin.com/rEmvZSiA

Multiset in Java

Here’s an implementation of a multiset in Java 8. It uses a Map<T, Integer> to count how many times an object was inserted (multiplicity). It is not thread-safe, but there’s synchronizedMultiset(...) and it always knows the current size in O(1). With the method asMap() you can get a view of the multiset as a Map, that will allow modification of the underlying multiset.

The code is on GitHub: github.com/claudemartin/multiset

This started as a simple implementation and is not rather complex. The iterator allows to remove elements during iteration. I tried to write my own Spliterator, but it wasn’t faster than the default implementaion. Many methods are optimized and I added some set operations for multisets (union, intersect, minus). With merge(...) you can merge two multisets with any operation.