skip-lists | 易学教程

Why Redis SortedSet uses Skip List instead of Balanced Tree?

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问题 The Redis document said as below : ZSETs are ordered sets using two data structures to hold the same elements in order to get O(log(N)) INSERT and REMOVE operations into a sorted data structure. The elements are added to a hash table mapping Redis objects to scores. At the same time the elements are added to a skip list mapping scores to Redis objects (so objects are sorted by scores in this "view"). I can not understand very much. Could someone give me a detailed explanation? 回答1: Antirez

Why Redis SortedSet uses Skip List instead of Balanced Tree?

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What is a zip tree, and how does it work?

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问题 I've heard of a new balanced BST data structure called a zip tree. What is the zip tree? How does it work? 回答1: At a high level, a zip tree is a randomized balanced binary search tree, that is a way of encoding a skiplist as a BST, and that uses a pair of operations called zipping and unzipping rather than tree rotations. The first bullet point - that zip trees are randomized, balanced BSTs - gives a feel for what a zip tree achieves at a high level. It's a type of balanced binary search tree

recursion function keeps running and prints nothing

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问题 Long story short, I'm supposed to make a code that inserts, deletes, searches for and prints numbers in a skip list with the first node being negative infinity and the last node being positive infinity (-inf > (...) > inf). I called my search function from my insert function to find a spot to insert any new nodes (only after the third node has been inserted) and I initialize or reference my nodes outside the main function rather than inside of it (although I'm debating on whether or not I

Expected space consumption of skip lists

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问题 What is the expected space used by the skip list after inserting n elements? I expect that in the worst case the space consumption may grow indeﬁnitely. Wikipedia says “Space O(n)”. How can this be proven one way or another? 回答1: According to this thesis, which I find more reliable then wikipedia, wikipedia is wrong . Probabilistic Skip List is Theta(nlogn) worst case space complexity. Despite the fact that on the average the PSL performs reasonably well, in the worst case its Theta(n lg n)

Skip Lists — ever used them?

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问题 I'm wondering whether anyone here has ever used a skip list. It looks to have roughly the same advantages as a balanced binary tree but is simpler to implement. If you have, did you write your own, or use a pre-written library (and if so, what was its name)? 回答1: Years ago I implemented my own for a probabilistic algorithms class. I'm not aware of any library implementations, but it's been a long time. It is pretty simple to implement. As I recall they had some really nice properties for

SkipList<T> vs Dictionary<TKey,TValue>

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问题 I've been reading about Skip Lists lately. I have a web application that executes quite complex Sql queries against static datasets. I want to implement a caching system whereby I generate an md5 hash of the sql query and then return a cached dataset for the query if it exists in the collection. Which algorithm would be better, Dictionary or a SkipList? Why? http://msdn.microsoft.com/en-us/library/ms379573%28VS.80%29.aspx#datastructures20_4_topic4 回答1: Dictionary , definitely. Two reasons:

Does java have a skip list implementation

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问题 I find ConcurrentSkipListSet in Java Collection Framework, which is backed up with a skip list. But is there a skip list in Java? A set does not work in my use case. I need a indexable list that supports duplicates. 回答1: Since you've mentioned a List that is both Indexable (I assume you want speedy retrieval) and need to allow duplicates, I would advise you go for a custom Set with a LinkedList or ArrayList perhaps. You need to have a base Set, an HashSet for example and keep adding values to

lock-free skiplist with rank operation

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问题 Is anyone aware of any lock-free skiplist implimentations and/or research papers that support the rank operation (i.e. find kth element)? Alternatively, is anyone aware of a fundamental reason why such an operation could never work? Bonus points: An implimentation that does not assume garbage collection. It has been my experience quite a few research papers ignore memory management. Support: For a description of how the rank operation may be done in a regular skiplist: "A Skip List Cookbook"

Finding All Intervals That Overlap a Point

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Consider a large set of floating-point intervals in 1-dimension, e.g. [1.0, 2.5], 1.0 |---------------|2.5 [1.5, 3.6], 1.5|---------------------|3.6 ..... It is desired to find all intervals that contain a given point. For example given point = 1.2, algorithm should return the first interval, and if given point = 2.0, it should return the first two interval in the above example. In the problem I am dealing, this operation needs to be repeated for a large number of times for a large number of intervals. Therefore a brute-force search is not desired and performance is an important factor. After