Computer Science Weekly Newsletter

Computer Science newsletter

Top new questions this week:

Why can humans solve certain "undecidable" problems?

High-order pattern matching is an undecidable problem. That means there is no algorithm that, given an equation a => b, where a and b are open terms on the simply typed lambda calculus, finds a ...

asked by srvm 13 votes
answered by D.W. 36 votes

Can a regular expression be infinite?

I know that languages which can be defined using regular expressions and those recognisable by DFA/NFA ( finite automata ) are equivalent. Also no DFA exists for the language $\{0^n1^n|n \ge 0\}$. ...

formal-languages regular-languages regular-expressions  
asked by sasha 7 votes
answered by Ran G. 22 votes

Complexity for finding a ball that maximizes the number of points lying in it

Given a set of points $x_1, \ldots, x_n \in \mathbb{R}^2$ and a radius $r$. Which is the complexity of finding the point with higher number of points at a distance smaller than $r$. E.g the one that ...

algorithms complexity-theory computational-geometry  
asked by Manuel 6 votes

Encrypting a 160-bit plaintext into a 160 bit ciphertext with a 128-bit block cipher

I have a field in my data store which must take exactly 160 bits of information. Some users will choose to make this data encrypted, some won't, so some of those 160 bit fields will be ciphertext some ...

cryptography encryption  
asked by Ayy Lmao 5 votes
answered by Gilles 5 votes

Time/Space Optimal k-Subset Operator Application - Is this a named problem?

I have searched extensively and unsuccessfully for references to a combinatorial problem that arises in my work. I am hoping someone can tell me if this type of problem has a "name" and provably ...

algorithms optimization combinatorics  
asked by bcbrock 5 votes
answered by Yuval Filmus 1 vote

What's the time complexity of this algorithm? And Why?

I am stuck by analyzing the time complexity of the following algorithm: def fun (r, k, d, p): if d > p: return r if d = 0 and p = 0: r <- r + k return r if d ...

algorithm-analysis runtime-analysis  
asked by xando 4 votes
answered by Yuval Filmus 5 votes

What is Least-Constraining-Value?

In constraint satisfaction problems, heuristics can be used to improve the performance of a bactracking solver. Three commonly given heuristics for simple backtracking solvers are: ...

artificial-intelligence constraint-satisfaction  
asked by zstewart 4 votes

Greatest hits from previous weeks:

Heap - Give an $O(n \lg k)$ time algorithm to merge $k$ sorted lists into one sorted list

Most probably, this question is asked before. It's from CLRS (2nd Ed) problem 6.5-8 -- Give an $O(n \lg k)$ time algorithm to merge $k$ sorted lists into one sorted list, where $n$ is the total ...

algorithms algorithm-analysis heaps priority-queues  
asked by ramgorur 4 votes
answered by Dukeling 6 votes

What is the novelty in MapReduce?

A few years ago, MapReduce was hailed as revolution of distributed programming. There have also been critics but by and large there was an enthusiastic hype. It even got patented! [1] The name is ...

algorithms distributed-systems parallel-computing algorithm-design  
asked by Raphael 45 votes
answered by Mike Samuel 36 votes

Can you answer these?

Difference between conflict serializability and view serializability

In my understanding both of them can be converted to serial schedules. (This helps with consistency by isolation property while also giving the performance boost by concurrency). I'm unable to ...

database-theory databases  
asked by aste123 1 vote

Binomial coefficient to approach multi-way choices DP problem?

I'm trying to understand this dynamic programming related problem, adapted from Kleinberg's Algorithm Design book. Not homework: i've already a solution, just considering if i'm ok with the theory. ...

asked by kentilla 1 vote

Using the random forest algorithm to predict vectors

I know this might sound like a newbie question, but bear with me. I have a large set of vectors in a migration pattern like so: I have read a paper where researchers use a random forest to predict ...

machine-learning trees randomized-algorithms neural-networks statistics  
asked by jeshaitan 2 votes
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