mgccl - Developer IT

Linux file association

- by Mgccl

With a desktop environment, there are file associations that goes with it. I'm a minimalistic user, who doesn't use any of such, but still want some kind of file associations to ease my burden. So I'm searching for a program that does something like the following. open file.pdf this will look at the extension, and translate to okular file.pdf. Of course one can always write a bash script to do this. I wonder if there is something existing, so I don't reinvent the wheel.

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Are there any CMS based on document-based database?

- by Mgccl

I did some googling, not much come up.

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Java creation of new set too slow

- by Mgccl

I have this program where it have some recursive function similar to this: lambda(HashSet<Integer> s){ for(int i=0;i<w;i++){ HashSet<Integer> p = (HashSet) s.clone(); p.addAll(get_next_set()); lambda(p); } } What I'm doing is union every set with the set s. And run lambda on each one of the union. I run a profiler and found the c.clone() operation took 100% of the time of my code. Are there any way to speed this up considerably?

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Check if a string substitution rule will ever generate another string.

- by Mgccl

Given two strings S and T of same length. Given a set of replacement rules, that find substring A in S and replace it with string B. A and B have the same length. Is there a sequence of rule application, such that it make string S into string T? I believe there is no better way to answer this than try every single rule in every single state. Which would be exponential time. But I don't know if there are better solutions to it.

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Really minimum lisp

- by Mgccl

What is the minimum set of primitives required such that a language is Turing complete and a lisp variant? Seems like car, cdr and some flow control and something for REPL is enough. It be nice if there is such list. Assume there are only 3 types of data, integers, symbols and lists.(like in picolisp)

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in-place permutation of a array follows this rule

- by Mgccl

Suppose there is an array, we want to find everything in the odd index, and move it to the end. Everything in the even index move it to the beginning. The relative order of all odd index items and all even index items are preserved. Suppose the values of the array, a[i] = i, n is even. Then we have. 0,1,2,3,4,5,...,n-1 after the operation 0,2,4,6,...,n-2,1,3,5,7,...,n-1 Can this be done in-place and in O(n) time?

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object construct a class of objects in java

- by Mgccl

There is a super class, A, and there are many subclasses, B,C,D... people can write more subclasses. Each of the class have the method dostuff(), each is different in some way. I want an object that constructs any object that belong to A or any of it's subclass. For example I can pass the name of the subclass, or a object of that class, and it will construct another object of the class. Of course I can write A construct(A var){ stuff = var.dostuff(); domorestuff(stuff) return new A(stuff); } B construct(B var){ stuff = var.dostuff(); domorestuff(stuff) return new B(stuff); } C construct(C var){ stuff = var.dostuff(); domorestuff(stuff) return new C(stuff); } but this is not efficient. I have to write a few new lines every time I make a new subclass. It seems I can't use generics either. Because I can't use dostuff() on objects not in any of the subclass of A. What should I do in this situation?

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Find the class of the generic object

- by Mgccl

Suppose I have the following class. public class gen<T> { public gen(){ } Class<T> class(){ //something that figures out what T is. } } How can I implement the class() function without pass any additional information? What I did is here, but I have to pass a object of T into the object gen. public class gen<T> { public gen(){ } Class<T> class(T var){ return (Class<T>) var.getClass(); } }

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