I'll be writing the online Google test tomorrow as a fresher. Apparently, they definitely ask one problem on Dynamic Programming?
Does anyone know of a good resource for collection of DP problems in C along with solutions? I know what DP is & have used it on an occasion or twice. However I feel to crack a DP problem in test, prior practice of typical problems will make it easier to approach.
Any good resources or problem sets with solutions in C will be highly appreciated. Thanks.
Okay, so I really hope this doesn't count as "shameless self-promotion," since all of these links are to code snippets I've posted on my personal site. If this is inappropriate, please let me know and I can take them down.
Here are a few fun DP problems that are pretty much classics:
Minimum edit distance: Given two strings A and B, find the shortest number of edits (insertions, deletions, or substitutions) necessary to convert A into B. This is called the Levenshtein distance. (My solution)
Optimal sequence alignment: Given two strings A and B, find the minimum number of gaps that must be inserted into the sequence to align A and B. This is called the Needleman-Wunsch algorithm. (My solution)
Single-source shortest paths: Given a directed graph G and a single node s, find the lengths of the shortest paths from s to each other node in the graph, assuming edges can be positive or negative but that no cycles exist. This is the Bellman-Ford algorithm. (My solution)
All-pairs shortest paths: Given a directed graph G, find the minimum distances between all pairs of nodes. This is the Floyd-Warshall algorithm. (My solution)
Hopefully this is somewhat useful, and best of luck tomorrow!
The Topcoder website is amazing. Not all of the problems use DP, but many do. Free full access to all problems from past competitions, which are at 3 different difficulty levels, as well as after-match explanations of every single problem from the problem author. Not only that, but you can quickly dig up the source code solution submitted by any coder in the competition.
Haven't been back there for a while, but they allow at least C++, Java, C# and I believe several other languages now.
I suggest u,collect a book "An Introduction to Bioinformatics Algorithms".This has a chapter fully on DP.As #templatetypedef mentioned Minimum edit distance,Optimal sequence alignment it has other problem with them.Though there is no implementation in it.You have to do it on your own.But you will find pretty interesting reading them.
To practice you can take one of the available problems at SPOJ. To recognize DP ones easily you can check at Problems Classifier (keyword: dp).
Related
I don't understand this issue:
Issue: HIS Metriken - Cyclomatic (CR-MET4): [function_name] 13>10
It appears in Klocwork analysis while checking the issues of Code: METRICS.E.HIS_Metriken___Cyclomatic__CR_MET4_
Can anyone support?
Thanks
Do you see all those ifs, elses, loops in that function?
Those are the problem, you need to either design this function's logic more elegantly or split it into more functions with well-defined purposes.
By the way, I can only see that problematic function of yours because I am especially clairvoyant. For this kind of question you should normally show your code, just to be fair towards all those other users which cannot read your mind like I did.
Naaa, not really. The cyclomatic complexity is a measure for number of potential paths through your function. And that you have crossed the treshold of 10 by 3 means your function must be full of control structs, which create many paths.
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 need to implement an intelligent agent to play Abalone game, for this kind of game the best way to proceed seems a min-max strategy with alpha beta pruning.
I have already implemented a naive search algorithm that use min-max with pruning,
my problem is...
How to generate the nodes of the tree where perform the search?
I have no idea of the right way to do this, and how assign the weigh to each node.
For generating the tree nodes: You need to implement a method that returns a collection of all possible legal moves given the current board position and the player whose turn it is. All these moves will become children of the node representing the current board position. Repeat until memory is exhausted to generate the game tree ;) or rather until you reach a reasonable tree depth.
For alpha-beta search you also need an evaluation function which calculates the weight for each board position/node. You can do some research or think about such a function yourself, maybe considering the number of stones still on the board. However a bad evaluation function can seriously screw up your results, so take care and run a lot of tests.
If you have trouble coming up with a reasonable evaluation function, I recommend you take a look into Monte-Carlo techniques such as UCT.
http://en.wikipedia.org/wiki/Monte_Carlo_tree_search
These tackle the problem using a probabilistic approach and have some nice advantages over alpha-beta. Also they don't require an evaluation function so you could skip this step.
Good luck!
I have published two libraries for move generation in Abalone. You didn't mention the programming language used for your search implementation, but you can easily port the functions.
For C++, https://sourceforge.net/projects/abnet/
For Python, https://gitlab.com/peer.sommerlund/haliotis
For an evaluation function, distance between all your marbles, or distance to their gravity center (same thing), works nicely. Tino Werner used this with a twist for his program that won ICGA 2003.
For understanding distance when using hex coordinates, I can recommend Amit Patel's page: https://www.redblobgames.com/grids/hexagons/
I am looking for some advice for a good way to detect either square or circular objects in an image. I currently have a canny edge algorithm running on the original greyscale and I can produce this output:
http://imgur.com/FAwowr1
Now I can see that there is a cubesat in this picture, but what is a good computationally efficient way that the program can see that aswell? I have looked at houghs transform but that seems to be very computation heavy. I have also looked at Harris corner detect, but I feel I would get to many false positives, for I am essentially looking to isolate pictures that contain said cube satellite.
Anyone have any thoughts on some good algorithms to pursue? I am very limited on space so I cannot use any large external libraries like opencv. (This is all in C btw)
Many Thanks!
I would into what is called mathematical morphology
Basically you operate on binary images, so you must find a clever way to threshold them first , the you do operations such as erosion and dilation with some well selected structuring element to extract areas of interest in your image.
I need to implement Minesweeper solver. I have started to implement rule based agent.
I have implemented certain rules. I have a heuristic function for choosing best matching rule for current cell (with info about surrounding cells) being treated. So for each chosen cell it can decide for 8 surroundings cells to open them, to mark them or to do nothing. I mean. at the moment, the agent gets as an input some revealed cell and decides what to do with surrounding cells (at the moment, the agent do not know, how to decide which cell to treat).
My question is, what algorithm to implement for deciding which cell to treat?
Suppose, for, the first move, the agent will reveal a corner cell (or some other, according to some rule for the first move). What to do after that?
I understand that I need to implement some kind of search. I know many search algorithms (BFS, DFS, A-STAR and others), that is not the problem, I just do not understand how can I use here these searches.
I need to implement it in a principles of Artificial Intelligence: A modern approach.
BFS, DFS, and A* are probably not appropriate here. Those algorithms are good if you are trying to plan out a course of action when you have complete knowledge of the world. In Minesweeper, you don't have such knowledge.
Instead, I would suggest trying to use some of the logical inference techniques from Section III of the book, particularly using SAT or the techniques from Chapter 10. This will let you draw conclusions about where the mines are using facts like "one of the following eight squares is a mine, and exactly two of the following eight squares is a mine." Doing this at each step will help you identify where the mines are, or realize that you must guess before continuing.
Hope this helps!
I ported this (with a bit of help). Here is the link to it working: http://robertleeplummerjr.github.io/smartSweepers.js/ . Here is the project: https://github.com/robertleeplummerjr/smartSweepers.js
Have fun!