skiplist | Go library for an efficient implementation
kandi X-RAY | skiplist Summary
kandi X-RAY | skiplist Summary
This Go-library implements a very fast and efficient Skiplist that can be used as direct substitute for a balanced tree or linked list. All basic operations ( Find, Insert and Delete) have approximate runtimes of O(log(n)) that prove real in benchmarks. For detailed API documentation, see the official docs: godoc.org/github.com/MauriceGit/skiplist. This implementation introduces a minimum amount of overhead and is tailored for maximum performance across all operations. In benchmarks, this skiplist is currently the fastest implementation in Go known to me. See a thorough benchmark of multiple skiplist implementations at: github.com/MauriceGit/skiplist-survey. All functions, be it Find, Insert or Delete that operate on first or last elements in the skiplist behave in near Constant time, no matter how many elements are already inserted in the skiplist. For real-world cases where elements are inserted or removed at random positions in the skiplist, we can clearly see the approximate O(log(n)) behaviour of the implementation which approximates to a constant value around 1800ns for Delete and 2200ns for Insert.
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Currently covering the most popular Java, JavaScript and Python libraries. See a Sample of skiplist
skiplist Key Features
skiplist Examples and Code Snippets
def __str__(self) -> str:
"""
:return: Visual representation of SkipList
>>> skip_list = SkipList()
>>> print(skip_list)
SkipList(level=0)
>>> skip_list.insert("Key1", "Va
def insert(self, key: KT, value: VT):
"""
:param key: Key to insert.
:param value: Value associated with given key.
>>> skip_list = SkipList()
>>> skip_list.insert(2, "Two")
>>&
def delete(self, key: KT):
"""
:param key: Key to remove from list.
>>> skip_list = SkipList()
>>> skip_list.insert(2, "Two")
>>> skip_list.insert(1, "One")
>>> skip
Community Discussions
Trending Discussions on skiplist
QUESTION
The Java ConcurrentSkipListMap
class contains a method randomLevel
that outputs the following, according to The Art of Multiprocessor Programming:
The
randomLevel()
method is designed based on empirical measurements to maintain the skiplist property. For example, in thejava.util.concurrent
package, for a maximal SkipList level of 31,randomLevel()
returns 0 with probability 3/4, i with probability 2^(−(i+2)) for i ∈ [1, 30], and 31 with probability 2^−32.
This looks like a geometric distribution, but not quite. Is there some way to neatly define this in terms of the provided random distributions, or do I have to do my own manipulation, as such:
...ANSWER
Answered 2022-Mar-04 at 11:08This looks like a geometric distribution, but not quite.
You are right, but problem is only probability of 0
. Note that you can use std::geometric_distribution
, by merging first two values into one.
QUESTION
A SkipList is a probabilistic data structure used, at least in part, for implementing an ordered key/value map. It is arranged in levels where higher levels skip nodes (the higher up, the more it skips), and the lowest level contains the nodes. As far as I have read, each level is implemented as a linked list, possibly a doubly linked list. And for some reason, skip lists are better for concurrency because in a multithreaded environment, they can be implemented without locks to enable fast/optimal performance as compared to say red/black trees or B+trees.
Here we have a "proper skip list" implemented in JavaScript, copied here for reference. The link has a nice suite of tests to show how it works.
...ANSWER
Answered 2022-Feb-25 at 14:17The summary of your question is:
- The meaning of group and node objects, and why they have their structure they do.
- What the nodes array is doing on a group.
I'll use an image taken from brilliant.org:
The linked lists appear as horizontal bands, while the arrays appear as vertical stacks.
A group corresponds to one distinct key in the set -- marked in yellow. The corresponding value is not depicted in the image, but is just payload and is not essential for understanding the data structure. A group has a nodes array -- displayed as a stack on top of the key. Each of these nodes belong to a different linked list in which they represent that same key. Those nodes have backreferences again to the group, so a node knows which key it represents, and which other linked lists have a node for this same key.
So the nodes array actually duplicates a key to different lists. One nodes array does not represent different keys in the collection -- just one. It is like an elevator to jump from one train (linked list) to another, with the same key.
The sizes of these arrays are randomly determined, but are intended to be small on average. This is driven by the stackUpProbability
. It represents the probability that an array is extended with one more node (upwards in the image). The probability for having at least one node (for a key) is obviously 1, but the probability that the array will have at least one more node in it (and thus have a size of at least 2), is stackUpProbability
. The probability that it will have size 3 is (stackUpProbability
)²... etc.
This way, the bottom linked list (at layerIndex
1) will have all keys in the collection (one node per key, in sorted order), but any next layer will have fewer keys, and the top layer might only have a hand full. The lists with fewer nodes provide a way to travel fast along the collection in search of a value. This provides a proximity of where a value could be found. Via the "elevator" a search algorithm can step down to lower (slower) linked lists and continue the search there, until it reaches the lowest level where the key will be found (if present), or where it would have been (if not).
QUESTION
is there a better way to do this, this code is working but i feel like there is a better way to do it
...ANSWER
Answered 2022-Feb-20 at 20:34Since you've already worked out how to build available
you could just zip
the two:
QUESTION
I encountered the error : error: ‘data_structure’ was not declared in this scope
,
when compile following codes.
I assume errors happened in :
root = data_structure.insert(root, data[data_ind]);
data_structure.insert(data[data_ind]);
TreapNode *res = data_structure.search(root, search_data[s_data_ind]);
bool res = data_structure.search(search_data[s_data_ind]);
But I don't know what I should correct.
complete codes : https://gist.github.com/theabc50111/05651b8c125feaaff5f80f15deb535f4
partial codes:
...ANSWER
Answered 2021-Dec-19 at 14:53The variables data_structure
and root
are alive and visible only in block scopes pf if statements where they are declared as for example in this if statement
QUESTION
Im a second year CS student and Im attempting to make a hangman game for fun during my winter break. Ive implemented the beginning of a menu class here, and yes I know this is too much oop for a project of this scope but I intent to reuse all these classes.
Anyways valgrind is telling me an Invalid read of size 8 and it returns the following lines in order:
menu::getName (menu.cpp:13) (this is at menu.cpp\getName()\return name;)
menu::print() (menu.cpp:21) (this is at menu.cpp\print()\cout<<". return to "
main (main.cppp:28) (this is at main.cpp\main()\thisMenu->print();)
Im usually very good at solving these types of problems, and I searched the web but I couldnt find a solution and Im completely stumped. I feel like it could be a simple issue and Im missing something but Im not sure. Any help is greatly appreciated! Thanks!
menu.cpp:
...ANSWER
Answered 2021-Dec-18 at 07:18If you look at this line:
QUESTION
I need to overload the ostream
operator with new functionality for a doubly linked Skip List class.
When I cout the instance of my class, I want it to iterate through my the levels of my skip list, and wherever the head
pointer is pointed to a nullptr
I want it to print the level name and a status of empty.
Would look something like:
...ANSWER
Answered 2021-Nov-03 at 21:59SkipList::maxLevels_;
refers to the static maxLevels_
member of the SkipList
class.
So, if you need maxLevels_
to be the maximum level of all the instances of SkipList
you have to declare it as static
.
Otherwise in your overloaded friend function you have to use the private member of the list
instance.
QUESTION
These days I am looking at skiplist code in Algorithms in C, Parts 1-4
, and when insert a new value into skiplist is more complex than I think. During insert, code should ensure that the new value insert into level i
with the probability of 1/2^i
, and this implement by below code:
ANSWER
Answered 2021-Oct-30 at 13:58Presumably RANDMAX
is intended to be RAND_MAX
.
Neglecting rounding issues, half the return values of rand
are above RAND_MAX / 2
, and therefore half the time, the loop exits with i
= 1.
If the loop continues, it updates i
to 2 and j
to 4. Then half the remaining return values (¾ of the total) are above RAND_MAX / 4
, so, one-quarter of the time, the loop exits with i
= 2.
Further iterations continue in the same manner, each iteration exiting with a portion of return values that is half the previous, until the lg_n_max
limit is reached.
Thus, neglecting rounding issues and the final limit, the routine returns 1 half the time, 2 one-quarter of the time, 3 one-eighth the time, and so on.
lg_n
is not defined in the routine. It appears to be a record of the greatest value returned by the routine so far.
QUESTION
I study the implementation of Redis, I know that there are two data structure (skiplist
and ziplist
) behind zset
. I know some basic idea of skiplist
(keep multiple pointer to access next element faster, avg time complexity of search is O(logN)).
My question is :
I read the info said that there are two situations that Redis will use skiplist
to implement zset
, first : there are many members in zset, second : memebers in zset
are long string
.
What's the benefit to use skiplist
instead of ziplist
in these two situations, why these two situations need special treatment? Why don't we always use one data structure to implement zset
?
ANSWER
Answered 2021-Apr-02 at 08:36ziplist is O(n) time complexity for searching and updating and skiplist is O(logN)
The only benefit for ziplist is memory usage. As zip list implement by linear memory address and no pointers to other nodes, it can save a lot of memory space for Redis.
When you only have few members in zset, O(N) and O(logN) will not have significant difference. But memory usage will have huge differences(consider you have 1m keys of zset and each zset only have 10 members).
And when there are a lot of members in zset(like 1m), time complexity is important since it will affect the concurrent performance.
QUESTION
I have a DXL script that open (read or edit) modules and put them in a skip list (so that I could close them at the end)
The skip list store the module handle of each module read or edit :
...ANSWER
Answered 2021-Mar-30 at 16:05Not sure if this is due to the excerpt you posted, but you should always turn off the autodeclare option and ensure that you always use the correct types for your variables by either checking the DXL manual or by using alternative sources like the "undocumented perms list" . data
performed on a ModuleVersion
returns type Module
. So you already have what you need. An alternative would be the perm bool open(ModName_ modRef)
. And note that the perm module
does not return a Module
, but a ModName_
.
Also, in addition to bool isRead(Module m)
, bool isEdit(Module m)
and bool isShare(Module m)
(!!) when you really want to close modules that have been opened previously, you might want to check bool unsaved(Module m)
QUESTION
When I tried to implement the SkipList by rust, I was trapped by the implement of Iterator
of Rc>
. Code is listed:
ANSWER
Answered 2021-Feb-27 at 15:02Is there a elegant implement of the Iterator for the Rc in Rust?
Not really. There's two big things in your way.
One limitation when building an Iterator
is that the output type cannot reference the iterator itself. It can either return an owned value (no lifetimes involved) or return references bound to the lifetime of some other object.
I see you've tried to communicate that you want to return Ref
s bound to the lifetime of the orignal SkipList
by using PhantomData<&'a K>
and also using 'a
in your Iterator::Item
. However, since your iterator can only source values from ptr
, an owned value with no lifetime-linkage to 'a
, the compiler will complain about mismatched lifetimes at one point or another.
In order to do this, your iterator would have to use something bound to 'a
, probably some form of Option<'a, _>>
.
However, another limitation is when you have nested RefCell
s, with each level that you iterate, you need to keep around an additional Ref
. The reason being that borrows from a Ref
don't keep the lifetime of the RefCell
, but from the Ref
itself.
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