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How do I find if a string contains a contiguous palindromic sequence ? I could try the naive solution in O(n^2) time where n is the string size , but any efficient algos to it ?
Well looking for just any palindrome isn't particularly interesting since every one character string is a palindrome. If you are looking for the longest palindrome you may be interested in Manacher's Algorithm.
A good description of the algorithm can be found here.
This is a quite common problem, and has ample results on google:
http://en.wikipedia.org/wiki/Longest_palindromic_substring
Rather than using Manacher's Algorithm you should use one of the parallel algorithms.
duplicate of : how to find longest palindromic subsequence?
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I am trying to build a question answering system where I have a set of predefined questions and their answers. For any given question from the user I have to find if the similar question already exists in the predefined questions and send answers. If it doesn't exist it has to reply a generic response. Any ideas on how to implement this using NLP would be really helpful.
Thanks in advance!!
As you have already mentioned in the question, this calls for a solution that computes text similarity. In this case question-question similarity. You have got a bunch of questions and for an incoming query/question, a similarity score has to be computed with every available question in hand. From a previous answer of mine, to do simple sentence similarity,
Convert the sentences into as suitable representation
Compute some of distance metric between the two representations and figure out the closest match
To achieve 1, you can consider converting every word in a sentence to corresponding vectors. There are libraries/algorithms like fasttext that provide vector mapping. A vector representation of the entire sentence is obtained by taking an average over all word vectors. Use cosine similarity to compute a score between the query and each question in the available list.
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I am trying to remove stop words before performing topic modeling. I noticed that some negation words (not, nor, never, none etc..) are usually considered to be stop words. For example, NLTK, spacy and sklearn include "not" on their stop word lists. However, if we remove "not" from these sentences below they lose the significant meaning and that would not be accurate for topic modeling or sentiment analysis.
1). StackOverflow is helpful => StackOverflow helpful
2). StackOverflow is not helpful => StackOverflow helpful
Can anyone please explain why these negation words are typically considered to be stop words?
Per IMSoP's advice above, please reference https://datascience.stackexchange.com/questions/15765/nlp-why-is-not-a-stop-word for the answer.
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I need to solve the following problem:
Give a linear-time algorithm to determine if a text T is a cyclic rotation of another string T'. For example, arc and car are cyclic rotations of each other.
I have no idea where to start. How can I solve this problem?
As a hint: if x and y have the same length, then x is a cyclic rotation of y iff x is a substring of yy. Try proving this and using this as the basis for your algorithm.
Hope this helps!
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I'm trying to write a python program that allows a user to input as many positive integers as they want. When the user inputs a positive or negative integer, the program generates a list of the inputted numbers that is sorted and also generates an average of the list inputted by the user.
Someone please help. I need to know this by this evening.
We don't do your homework here, but without divulging a complete solution, think about writing a loop to query the user for integers and add them to a Python list. You can make use of the sorted() and sort() functions in Python to sort your data. Averaging values in a list is trivial and can be easily found online or with basic programming knowledge (sum the values in the list and divide that total by the length of the list). Also beware of integer division depending on your version of Python.
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Given a set of 10 symbols and a set of strings(at max 100) of length at max 20 each consisting of these symbols, find the maximum length string which can be made from these symbols that doesn't have any of the given strings as its sub-string. In case, if we can have infinite long string satisfying the property, print -1.
Besides brute force algorithm which will go exponential in time, I am not able to get any solution for this.
Any hint to approach this problem will be thankful.
Given a set of strings that need to be matched, my immediate reaction is to use http://en.wikipedia.org/wiki/Aho%E2%80%93Corasick_string_matching_algorithm to create a matcher. This matcher is a finite state machine that accepts one character at a time and tells you which state you end up in next, given that character.
So I think you can reduce the problem to accepting a directed graph and a starting point and finding the longest route through that graph that does not go through the nodes that correspond to pattern matches - which I think we can simply delete from the graph. This is covered in http://en.wikipedia.org/wiki/Longest_path. Constructing this graph is also linear so the whole thing seems to be O(n)