avl_array | High performance templated AVL tree using a fixed size array | Hashing library
kandi X-RAY | avl_array Summary
kandi X-RAY | avl_array Summary
avl_array is a templated C++ (STL map like) container class that stores key-value data organzied as AVL-tree in a fixed size array. For an embedded project I needed a high-performance key-value store in static memory with the fastest key retrieval time I could get. Normally a std::map container with a static custom allocator is taken, but std::map pulls a lot of unwanted stuff and dependencies into the project while its performance is rather average. That being said, motivation of this container is to insert, update, delete and find random key-value elements in static allocated memory with highest performance and in a minimum of time. It might also be the base class for an associative array container.
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avl_array Examples and Code Snippets
Lines of Code : 25License : Permissive (MIT)
Copy#include
// create a 2048 node tree with as key and value types and as size type in 'Fast' mode
avl_array avl;
// insert
avl.insert(1, 1); // set value of key 1 to 1
avl.insert(2, 2); // set value of key 2 to 2
avl.insert(3, 3); // set val Community Discussions
Trending Discussions on Hashing
QUESTION
I am using Perceptual hashing technique to find near-duplicate and exact-duplicate images. The code is working perfectly for finding exact-duplicate images. However, finding near-duplicate and slightly modified images seems to be difficult. As the difference score between their hashing is generally similar to the hashing difference of completely different random images.
To tackle this, I tried to reduce the pixelation of the near-duplicate images to 50x50 pixel and make them black/white, but I still don't have what I need (small difference score).
This is a sample of a near duplicate image pair:
Image 1 (a1.jpg):
Image 2 (b1.jpg):
The difference between the hashing score of these images is : 24
When pixeld (50x50 pixels), they look like this:
rs_a1.jpg
rs_b1.jpg
The hashing difference score of the pixeled images is even bigger! : 26
Below two more examples of near duplicate image pairs as requested by @ann zen:
Pair 1
Pair 2
The code I use to reduce the image size is this :
...ANSWER
Answered 2022-Mar-22 at 12:48Rather than using pixelisation to process the images before finding the difference/similarity between them, simply give them some blur using the cv2.GaussianBlur() method, and then use the cv2.matchTemplate() method to find the similarity between them:
QUESTION
I'm implementing my own class, with custom __eq__. And I'd like to return True for things that are not "equal" in a mathematical sense, but "match" in a fuzzy way.
An issue with this is, however, that this leads to loss of transitivity in a mathematical sense, i.e. a == b && b ==c, while a may not be equal to c.
Question: is Python dependent on __eq__ being transitive? Will what I'm trying to do break things, or is it possible to do this as long as I'm careful myself not to assume transitivity?
I want to match telephone numbers with one another, while those may be either formatted internationally, or just for domestic use (without a country code specified). If there's no country code specified, I'd like a number to be equal to a number with one, but if it is specified, it should only be equal to numbers with the same country-code, or without one.
So:
- Of course,
+31 6 12345678should equal+31 6 12345678, and06 12345678should equal06 12345678 +31 6 12345678should equal06 12345678(and v.v.)+49 6 12345678should equal06 12345678(and v.v.)- But
+31 6 12345678should not be equal to+49 6 12345678
Edit: I don't have a need for hashing (and so won't implement it), so that at least makes life easier.
...ANSWER
Answered 2022-Mar-14 at 18:06There is no MUST but a SHOULD relation for comparisons being consistent with the commonly understood relations. Python expressively does not enforce this and float is an inbuilt type with different behaviour due to float("nan").
Expressions: Value comparisons[…]
User-defined classes that customize their comparison behavior should follow some consistency rules, if possible:
- […]
- Comparison should be symmetric. In other words, the following expressions should have the same result:
x == yandy == xx != yandy != xx < yandy > xx <= yandy >= x- Comparison should be transitive. The following (non-exhaustive) examples illustrate that:
- x > y and y > z implies x > z
- x < y and y <= z implies x < z
Python does not enforce these consistency rules. In fact, the not-a-number values are an example for not following these rules.
Still, keep in mind that exceptions are incredibly rare and subject to being ignored: most people would treat float as having total order, for example. Using uncommon comparison relations can seriously increase maintenance effort.
Canonical ways to model "fuzzy matching" via operators are as subset, subsequence or containment using unsymmetric operators.
- The
setandfrozensetsupport>,>=and so on to indicate that one set encompases all values of another.
QUESTION
I know that in hashing you, by definition, lose information. However, as email addresses can be restricted - such as with the information available I would know a potential domain of the email, and that it must have an @. Do these constraints change anything about the problem? Or is the best way to simply make a guess and see if the hash is the same? Also MD5 is no longer as secure as it once was.
Thanks
...ANSWER
Answered 2022-Feb-15 at 15:55That is the point of Md5 hashing that even a minute change in the string can change the hash completely. So these constraints change nothing about the problem.
However since you said that its an email and that you know about the potential domain then you can try this technique.
- Generate a list of potential emails it will be within 26 letters and lets say of maximum size 10.
Then you can generate an md5 for all of these possibilities and check if it is equal to the one you have.
QUESTION
I'm trying to learn Go while writing a small program. The program should parse a PATH recursivelys as efficient and fast as possible and output the full filename (with the path included) and the sha256 file hash of the file.
If the file hashing generates fails, I wanna keep the error and add it to the string (at the hash position).
The result should return a string on the console like: fileXYZ||hash
Unfortunately, the programs hangs at some point. I guess some of my channels are not closing properly and waiting indefinitely for input. I've been trying for quite some time to fix the problem, but without success.
Does anyone have an idea why the output hangs? Many many thx in advance, any input/advice for a Go newcomer is welcome too ;-).
(I wrote separate functions as I wanna add additional features after having fixed this issue.)
Thanks a lot! Didier
Here is the code:
...ANSWER
Answered 2022-Jan-29 at 19:46The following loop hangs because chashes is not closed.
QUESTION
Assume we have two tables (think as in SQL tables), where the primary key in one of them is the foreign key in the other. I'm supposed to write a simple algorithm that would imitate the joining of these two tables. I thought about iterating over each element in the primary key column in the first table, having a second loop where it checks if the foreign key matches, then store it in an external array or list. However, this would take O(N*M) and I need to find something better. There is a hint in the textbook that it involves hashing, however, I'm not sure how hashing could be implemented here or how it would make it better?
Editing to add an example:
...ANSWER
Answered 2021-Dec-24 at 22:18Read the child table's primary and foreign keys into a map where the keys are the foreign keys and the values are the primary keys. Keep in mind that one foreign key can map to multiple primary keys if this is a one to many relationship.
Now iterate over the primary keys of the mother table and for each primary key check whether it exists in the map. If so, you add a tuple of the primary keys of the rows that have a relation to the array (or however you want to save it).
The time complexity is O(n + m). Iterate over the rows of each table once. Since the lookup in the map is constant, we don't need to add it.
Space complexity is O(m) where m is the number of rows in the child table. This is some additional space you use in comparison to the naive solution to improve the time complexity.
QUESTION
I'm seeking advice from people deeply familiar with the binary layout of Apache Parquet:
Having a data transformation F(a) = b where F is fully deterministic, and same exact versions of the entire software stack (framework, arrow & parquet libraries) are used - how likely am I to get an identical binary representation of dataframe b on different hosts every time b is saved into Parquet?
In other words how reproducible Parquet is on binary level? When data is logically the same what can cause binary differences?
- Can there be some uninit memory in between values due to alignment?
- Assuming all serialization settings (compression, chunking, use of dictionaries etc.) are the same, can result still drift?
I'm working on a system for fully reproducible and deterministic data processing and computing dataset hashes to assert these guarantees.
My key goal has been to ensure that dataset b contains an idendital set of records as dataset b' - this is of course very different from hashing a binary representation of Arrow/Parquet. Not wanting to deal with the reproducibility of storage formats I've been computing logical data hashes in memory. This is slow but flexible, e.g. my hash stays the same even if records are re-ordered (which I consider an equivalent dataset).
But when thinking about integrating with IPFS and other content-addressable storages that rely on hashes of files - it would simplify the design a lot to have just one hash (physical) instead of two (logical + physical), but this means I have to guarantee that Parquet files are reproducible.
I decided to continue using logical hashing for now.
I've created a new Rust crate arrow-digest that implements the stable hashing for Arrow arrays and record batches and tries hard to hide the encoding-related differences. The crate's README describes the hashing algorithm if someone finds it useful and wants to implement it in another language.
I'll continue to expand the set of supported types as I'm integrating it into the decentralized data processing tool I'm working on.
In the long term, I'm not sure logical hashing is the best way forward - a subset of Parquet that makes some efficiency sacrifices just to make file layout deterministic might be a better choice for content-addressability.
...ANSWER
Answered 2021-Dec-05 at 04:30At least in arrow's implementation I would expect, but haven't verified the exact same input (including identical metadata) in the same order to yield deterministic outputs (we try not to leave uninitialized values for security reasons) with the same configuration (assuming the compression algorithm chosen also makes the deterministic guarantee). It is possible there is some hash-map iteration for metadata or elsewhere that might also break this assumption.
As @Pace pointed out I would not rely on this and recommend against relying on it). There is nothing in the spec that guarantees this and since the writer version is persisted when writing a file you are guaranteed a breakage if you ever decided to upgrade. Things will also break if additional metadata is added or removed ( I believe in the past there have been some big fixes for round tripping data sets that would have caused non-determinism).
So in summary this might or might not work today but even if it does I would expect this would be very brittle.
QUESTION
I have an Angular 12 application that has different build environments (dev/staging/prod) and I have configured these with output hashing on in angular.json:
ANSWER
Answered 2021-Nov-25 at 08:51In case you're using a service worker (eg @angular/pwa which installs @angular/service-worker along), you're entire angular app is being cached by the browser. This includes index.html + all javascript files + all stylesheets.
To have a new version of your application pushed to your users, you have to do 2 things:
Update your ngsw-config.json on each new release:
QUESTION
Trying to understand how to get and then save user in client (using JWT token in Http only cookie), so that I can do conditional rendering. What I'm having difficulty with is how to continously know if the user is logged in or not, without having to send a request to the server each time the user changes/refresh page. (Note: the problem is not how do I get the token in the Http only cookie, I know that this is done through withCredentials: true)
So my problem is how do you get/store the access token so that the client will not have to make a request to the server each time the user does something on the website. For example the Navbar should do conditional renderingen depending on if the user is logged in or not, then I don't want to do "ask the server if the user has a access token, then if not check if user has refresh token, then return a new access token if true else redirect to login page" every single time the user switches page.
Client:
UserContext.js
...ANSWER
Answered 2021-Nov-16 at 08:54Do I really need to do a request to the server each time the user switches page or refresh page?
That is the safest way. If you want to keep with the current security best practices for SPAs, then using http-only, secure, same-site cookies is the best option. Refreshes won't happen that often on your page, so it shouldn't be a problem.
My initial idea was to use useEffect in the App component where I make a call to the function GetUser() which makes a request to "/get-user" which will user the refreshToken to find the user
What I would do is to first verify the access token, if it's valid then take the userId out of the access token (if you don't have it there you can easily add it as you're creating the tokens manually) and read the user data from the database. If the access token is invalid then return an error to the website and let the user use the refresh token to get a new access token. So I wouldn't mix responsibilities here - I wouldn't use refresh token to get information about the logged in user.
Also I have a question about when I should be calling "/token" in the server to create new access tokens. Should I always try to use the access token to do things that require authentication and if it for example returns null at some point then I make request to "/token" and after that repeat what the user was trying to do?
Yes, that's how it usually is implemented. You make a call with the access token to a protected endpoint. It would be best if the endpoint returned 401 response if the token is expired or invalid. Then your app knows that it should use the refresh token to get a new access token. Once you have a new access token you try to make the call to the protected endpoint again. If you don't manage to get a new access token (e.g. because the refresh token has expired), then you ask the user to log in again.
QUESTION
I need web app with base url as
...ANSWER
Answered 2021-Oct-22 at 07:31I'd advice you commenting out href in 'web/index.html' (platform project automatically generated when adding Web). That's how I did it:
https://github.com/maxim-saplin/flutter_web_spa_sample/blob/main/web/index.html
And here's the example of this app working under virtual directory: https://maxim-saplin.github.io/flutter_web_spa_sample/html/#/
Flutter Web somehow has these silly issues in scaffolding for the web project (href in index.html, wrong paths for service worker etc.) - discovered this while playing with GitHub pages.
QUESTION
I have an Ionic project I'm working with that is having trouble building to Android. I inherited this project, so that's why I'm not 100% familiar with Fastlane and how it's building the java files. Additionally, I'm on WSL2 and using sdkmanager with the following installed packages:
...ANSWER
Answered 2021-Sep-19 at 15:32cordova-plugin-androidx-adapter will migrate older libraries to use AndroidX Support Libraries automatically. I believe this is needed when you target Android 10 or higher, which is when the switch was made. Once all of your plugins support AndroidX, you can remove the adapter plugin.
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