Hello I am trying to implement the OPT Page Replacement algorithm:
Currenly I have created a linked list for all the future memory access references.
And my initial idea was to compare each reference in my linked list and mark down the distance for its next appearence as an attribute. When actually running the program and a page fault happens, I will look through every page in my page table and evict the page that has the longest distance.
However, I find my idea quite complicated and inefficient to implement. Is there a simplier way to implement this algorithm? Thanks.
The swaps made are the same for these two executions: (1) OPT on the original sequence of requests (2) LRU on the sequence of requests in reverse order. You can implement LRU via the doubly-linked-list strategy outlined in the linked Wikipedia article.
Related
I'm taking a class in data structures and was given the assignment to find the shortest path through a maze using C and implementing the queue data structure. However, I can't really wrap my head around how to use a queue here.
I know the idea is to count every possible move from the start position, and when you hit the target, you're supposed to trace back to the initial position. This is what I don't understand. Because if I use a queue and delete all the moves that leads up to the target, I have no data to use to do the trace back, and if I don't delete the moves that lead to the target (i.e. saving all the possible moves and deleting them when I actually do the trace back), I might as well be using a stack.
I know there's something I don't quite get, but I can't figure out what it is. How would I utilize the queue data structure in this case?
What your professor is trying to get you to use is called "breadth-first search". The queue comes in for deciding which spaces to explore next. When you are looking at the possible paths to take, you enqueue all the paths you have yet to explore. Instead of continuing down the path you're on (which would be "depth-first search"), you dequeue the next spot you need to check, which will take you back to one of the positions you were considering earlier.
The actual implementation is up to you, I'd recommend looking for examples of breadth-first search online.
This might be frivolous question, so please have understanding for my poor soul.
After reading this article about Intelligent Design sort (http://www.dangermouse.net/esoteric/intelligentdesignsort.html) which is in no way made to be serious in any way, I started wondering whether this could be possible.
An excerpt from article says:
The probability of the original input list being in the exact order it's in is 1/(n!). There is such a small likelihood of this that it's clearly absurd to say that this happened by chance, so it must have been consciously put in that order by an intelligent Sorter.
Let's for a second forget about intelligent Sorter, and think about possibility that random occurrences of members in array are in some way sorted. Our algorithm should determine the pattern without changing array's structure.
Is there any way to do this? Speed is not a requirement.
The implementation is very easy actually. The entire point of the article is that you don't actually sort anything. In other words, a correct implementation is a simple NOP. As my preferred language is Java, I'll show a simple in-place implementation in Java as a lambda function:
list->{}
Funny article, I had a good laugh.
If the only thing you're interested in is that whether your List is sorted, then you could simply keep an internal sorted flag (defaulted to true for an empty list) and override your add() method to check if the element you're adding fits the ordering of the List - that is, compare it to the adjacent elements and setting the sorted flag appropriately.
I am currently trying to implement OWL2 RL via Rete algorithm. I have run into the following issue: How to implement lists needed for example in this rule: eq-diff2 (W3C reccomendation)?
Thanks.
I have developed this solution.
Before inference construct the lists in memory. It is simple,
because the elements can be easily identified.
Construct RETE nodes for first m rules, which don't need "loop" construct
Put an action in the last node:
Add new Rete (alpha+beta) nodes for the corresponding list (you will always know which, because it's one of the "static" rules)
Put corresponding WMEs into newly created alpha memories
Activate Beta nodes
It is probably possible to remove the whole "dynamic" branch after the final action is performed.
Can we randomly access a point in a CvSeq object? We can traverse it, so I imagine it's possible in a simple manner. How is this accomplished?
I have found it. There is a method called cvGetSeqElem, which takes in the sequence and the index. Thanks for the help though. This might just follow the linked list linearly, but it's simpler than manually coding the search.
Looking at the OpenCV API (http://opencv.willowgarage.com/documentation/dynamic_structures.html) it doesn't sound possible. Looks to be some form of linked list implementation, which means that the only way to access an element part way though is to follow the links.
cvSeq is a linked list - you have to follow the chain of links, you have no idea where the next entry is stored in memory.
I was thinking to implement MD5 as a code kata and wanted to use BDD to drive the design (I am a BDD newb).
However, the only test I can think of starting with is to pass in an empty string, and the simplest thing that will work is embedding the hash in my program and returning that.
The logical extension of this is that I end up embedding the hash in my solution for every test and switching on the input to decide what to return. Which of course will not result in a working MD5 program.
One of my difficulties is that there should only be one public function:
public static string MD5(input byte[])
And I don't see how to test the internals.
Is my approach completely flawed or is MD5 unsuitable for BDD?
I believe you chose a pretty hard exercise for a BDD code-kata. The thing about code-kata, or what I've understood about it so far, is that you somehow have to see the problem in small incremental steps, so that you can perform these steps in red, green, refactor iterations.
For example, an exercise of finding an element position inside an array, might be like this:
If array is empty, then position is 0, no matter the needle element
Write test. Implementation. Refactor
If array is not empty, and element does not exist, position is -1
Write test. Implementation. Refactor
If array is not empty, and element is the first in list, position is 1
Write test. Implementation. Refactor
I don't really see how to break the MD5 algorithm in that kind of steps. But that may be because I'm not really an algorithm guy. If you better understand the steps involved in the MD5 algorithm, then you may have better chances.
It depends on what you mean with unsuitable... :-) It is suitable if you want to document a few examples that describes your implementation. It should also be possible to have the algorithm emerge from your specifciation if you add one more character for each test.
By just adding a switch statement you're just trying to "cheat the system". Using BDD/TDD does not mean you have to implement stupid things. Also the fact that you have hardcoded hash values as well as a switch statement in your code are clear code smells and should be refactored and removed. That is how your algorithm should emerge because when you see the hard coded values you first remove them (by calculating the value) and then you see that they are all the same so you remove the switch statement.
Also if your question is about finding good katas I would recommend lokking in the Kata catalogue.