Closed. This question needs details or clarity. It is not currently accepting answers.
Want to improve this question? Add details and clarify the problem by editing this post.
Closed 2 years ago.
Improve this question
Design an algorithm to determine how many numbers are in a string. Example, given the string "Hello people from the 4 worlds, this is my only 1 program", the output must be 2.
Basically you need to write a simple parser to parse out the numbers in your string. To do that you need to be able to recognise a number correctly, which is a little more complicated than just recognising digits. Something like "-12,348.971" is a number, but contains the characters -,. which are not digits. However, the string "-,." is not itself a number.
Read through the string, character by character. When the parser finds the start of a number, count one more number found, and read through all the characters that form that number. Read '123' as a single number, not three numbers. When you reach the end of the number skip over non-number characters until either you find the next number or you reach the end of the file.
You might want to read up on writing a simple parser in the language of your choice.
Related
Closed. This question needs details or clarity. It is not currently accepting answers.
Want to improve this question? Add details and clarify the problem by editing this post.
Closed 6 months ago.
Improve this question
So I've got a list of positive integers and I want to combine all elements into one unique integer. But I am only able to use basic arithmetic (+, -, *, /).
The result should have the semantics of a hash for the input sequence. So no other sequence should be able to produce it.
Any suggestions how I could tackle this problem?
Interpreting "hash" to mean that the output domain is bounded, it's not possible to "hash" an unbounded input sequence to a unique output. Those numbers can only be compressed so much without losing information.
If this were possible, compression ratios for any digital information could approach infinity.
Closed. This question needs details or clarity. It is not currently accepting answers.
Want to improve this question? Add details and clarify the problem by editing this post.
Closed 5 years ago.
Improve this question
I have a situation where I need to grab a large number from a string. The two cases I'm working with are:
1) when the number is made up of only numbers, like 265038960
2) When the number has a letter appended to it, like 69235M
I've been using the regex pattern
(\d.+)[A-Z]
This works for the second case and grabs '69235' without the 'M', but breaks on the first case where a letter is not found.
How can I use a condition within the regex to only parse out the number whether or not a letter is present at the end of the string?
(\d+[A-Z]?) # capture any number of digits, together with 0 or 1 uppercase letter
It's not clear if you want to capture the letter or not. In the case you want to dispose of the letter:
(\d+)[A-Z]? # capture any number of digits, followed by 0 or 1 uppercase letter
Look at example
Closed. This question needs to be more focused. It is not currently accepting answers.
Want to improve this question? Update the question so it focuses on one problem only by editing this post.
Closed 6 years ago.
Improve this question
On what language is more easy to code that kind of algorithm and make it more flexible to changes.
It's pretty easy to do, at least in widely used programming languages that I'm aware of (e.g. C++, Java, etc).
Store all possible characters in an ordered collection like array or a string. For example, you can make a string that contains all letters and digits like so:
// Exact syntax depends on your programming language.
//
// I used a string for simplicity here but some languages don't allow
// you to access individual string characters so you'll need an array.
//
string a = "abcdefghijklmnopqrstuvwxyz0123456789";
Generate a random number between 0 and length(a) - 1 (size of your character set array minus one).
Use the number you generated as an index and extract the character from the array at that index.
Congratulations! You've just generated one random character from your character set. Go back to step #2 and repeat N - 1 times (N is here the total number of characters you want to generate).
Closed. This question needs to be more focused. It is not currently accepting answers.
Want to improve this question? Update the question so it focuses on one problem only by editing this post.
Closed 6 years ago.
Improve this question
My problem is simple: I have a database containing 400,000 substrings (movies and tv shows titles).
I'd like to match these titles in a message such as:
I really love Game Of Thrones and Suits, also Spotlight is an awesome
movie.
What I need is to match Game Of Thrones, Suits and Spotlight in this string.
I tried to send all titles to wit.ai but it seems that it can't handle 100,000 substrings.
I'm wondering if elasticsearch could do the job?
If that's a common problem, sorry, could you help me to search in the right direction.
Thanks!
One of the best algorithms to find strings from dictionary in a text is Aho-Corasick one
dictionary-matching algorithm that locates elements of a finite set of
strings (the "dictionary") within an input text. It matches all
strings simultaneously. The complexity of the algorithm is linear in
the length of the strings plus the length of the searched text plus
the number of output matches.
But I wonder that your database engine does not provide possibilities for such searching... Probably it really can, but you don't know?
Closed. This question needs to be more focused. It is not currently accepting answers.
Want to improve this question? Update the question so it focuses on one problem only by editing this post.
Closed 7 years ago.
Improve this question
Is there an algorithm for handling secret words without storing them in clear text or using a reversible encryption?
Necessary operations include
getting the length of it, so that we can generate indexes
testing whether the n-th character matches a specific character
If you want to match the n-th character with another character, the encryption becomes easily reversible. An adversary just has to test all characters with all possible values. So in ASCII that will be 256*8=2048 for an 8 character password.
You should normally store a SHA-256 or SHA-512 of the password (possibly prefixed with a random salt) and compare this value against the user inputed value SHA-256/512ed.
You can also repeat the SHA-256/512 operations several thousand times to make attacks more difficult.