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  • reconstructing a tree from its preorder and postorder lists.

    - by NomeN
    Consider the situation where you have two lists of nodes of which all you know is that one is a representation of a preorder traversal of some tree and the other a representation of a postorder traversal of the same tree. I believe it is possible to reconstruct the tree exactly from these two lists, and I think I have an algorithm to do it, but have not proven it. As this will be a part of a masters project I need to be absolutely certain that it is possible and correct (Mathematically proven). However it will not be the focus of the project, so I was wondering if there is a source out there (i.e. paper or book) I could quote for the proof. (Maybe in TAOCP? anybody know the section possibly?) In short, I need a proven algorithm in a quotable resource that reconstructs a tree from its pre and post order traversals. Note: The tree in question will probably not be binary, or balanced, or anything that would make it too easy. Note2: Using only the preorder or the postorder list would be even better, but I do not think it is possible. Note3: A node can have any amount of children. Note4: I only care about the order of siblings. Left or right does not matter when there is only one child.

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  • Good implementations of reinforced learning?

    - by Paperino
    For an ai-class project I need to implement a reinforcement learning algorithm which beats a simple game of tetris. The game is written in Java and we have the source code. I know the basics of reinforcement learning theory but was wondering if anyone in the SO community had hands on experience with this type of thing. What would your recommended readings be for an implementation of reinforced learning in a tetris game? Are there any good open source projects that accomplish similar things that would be worth checking out? Thanks in advanced Edit: The more specific the better, but general resources about the subject are welcomed. Follow up: Thought it would be nice if I posted a followup. Here's the solution (code and writeup) I ended up with for any future students :). Paper / Code

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  • Programmer Puzzle: Encoding a chess board state throughout a game

    - by Andrew Rollings
    Not strictly a question, more of a puzzle... Over the years, I've been involved in a few technical interviews of new employees. Other than asking the standard "do you know X technology" questions, I've also tried to get a feel for how they approach problems. Typically, I'd send them the question by email the day before the interview, and expect them to come up with a solution by the following day. Often the results would be quite interesting - wrong, but interesting - and the person would still get my recommendation if they could explain why they took a particular approach. So I thought I'd throw one of my questions out there for the Stack Overflow audience. Question: What is the most space-efficient way you can think of to encode the state of a chess game (or subset thereof)? That is, given a chess board with the pieces arranged legally, encode both this initial state and all subsequent legal moves taken by the players in the game. No code required for the answer, just a description of the algorithm you would use. EDIT: As one of the posters has pointed out, I didn't consider the time interval between moves. Feel free to account for that too as an optional extra :) EDIT2: Just for additional clarification... Remember, the encoder/decoder is rule-aware. The only things that really need to be stored are the player's choices - anything else can be assumed to be known by the encoder/decoder. EDIT3: It's going to be difficult to pick a winner here :) Lots of great answers!

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  • Fastest sorting algorithm for a specific situation

    - by luvieere
    What is the fastest sorting algorithm for a large number (tens of thousands) of groups of 9 positive double precision values, where each group must be sorted individually? So it's got to sort fast a small number of possibly repeated double precision values, many times in a row. The values are in the [0..1] interval. I don't care about space complexity or stability, just about speed.

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  • Determining whether values can potentially match a regular expression, given more input

    - by Andreas Grech
    I am currently writing an application in JavaScript where I'm matching input to regular expressions, but I also need to find a way how to match strings to parts of the regular expressions. For example: var invalid = "x", potentially = "g", valid = "ggg", gReg = /^ggg$/; gReg.test(invalid); //returns false (correct) gReg.test(valid); //returns true (correct) Now I need to find a way to somehow determine that the value of the potentially variable doesn't exactly match the /^ggg$/ expression, BUT with more input, it potentially can! So for example in this case, the potentially variable is g, but if two more g's are appended to it, it will match the regular expression /^ggg$/ But in the case of invalid, it can never match the /^ggg$/ expression, no matter how many characters you append to it. So how can I determine if a string has or doesn't have potential to match a particular regular expression?

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  • Graph Algorithm To Find All Paths Between N Arbitrary Vertices

    - by russtbarnacle
    I have an graph with the following attributes: Undirected Not weighted Each vertex has a minimum of 2 and maximum of 6 edges connected to it. Vertex count will be < 100 I'm looking for paths between a random subset of the vertices (at least 2). The paths should simple paths that only go through any vertex once. My end goal is to have a set of routes so that you can start at one of the subset vertices and reach any of the other subset vertices. Its not necessary to pass through all the subset nodes when following a route. All of the algorithms I've found (Dijkstra,Depth first search etc.) seem to be dealing with paths between two vertices and shortest paths. Is there a known algorithm that will give me all the paths (I suppose these are subgraphs) that connect these subset of vertices?

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  • Do you still limit line length in code?

    - by Noldorin
    This is a matter on which I would like to gauge the opinion of the community: Do you still limit the length of lines of code to a fixed maximum? This was certainly a convention of the past for many languages; one would typically cap the number of characters per line to a value such as 80 (and more recnetly 100 or 120 I believe). As far as I understand, the primary reasons for limiting line length are: Readability - You don't have to scroll over horizontally when you want to see the end of some lines. Printing - Admittedly (at least in my experience), most code that you are working on does not get printed out on paper, but by limiting the number of characters you can insure that formatting doesn't get messed up when printed. Past editors (?) - Not sure about this one, but I suspect that at some point in the distant past of programming, (at least some) text editors may have been based on a fixed-width buffer. I'm sure there are points that I am still missing out, so feel free to add to these... Now, when I tend to observe C or C# code nowadays, I often see a number of different styles, the main ones being: Line length capped to 80, 100, or even 120 characters. As far as I understand, 80 is the traditional length, but the longer ones of 100 and 120 have appeared because of the widespread use of high resolutions and widescreen monitors nowadays. No line length capping at all. This tends to be pretty horrible to read, and I don't see it too often, though it's certainly not too rare either. Inconsistent capping of line length. The length of some lines are limited to a fixed maximum (or even a maximum that changes depending on the file/location in code), while others (possibly comments) are not at all. My personal preference here (at least recently) has been to cap the line length to 100 in the Visual Studio editor. This means that in a decently sized window (on a non-widescreen monitor), the ends of lines are still fully visible. I can however see a few disadvantages in this, especially when you end up writing code that's indented 3 or 4 levels and then having to include a long string literal - though I often take this as a sign to refactor my code! In particular, I am curious what the C and C# coders (or anyone who uses Visual Studio for that matter) think about this point, though I would be interested in hearing anyone's thoughts on the subject. Edit Thanks for the all answers - I appreciate the variety of opinions here, all presenting sound reasons. Consensus does seem to be tipping in the direction of always (or almost always) limit the line length. Interestingly, it seems to be in various coding standards to limit the line length. Judging by some of the answers, both the Python and Google CPP guidelines set the limit at 80 chars. I haven't seen anything similar regarding C# or VB.NET, but I would be curious to see if there are ones anywhere.

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  • Genetic Programming Online Learning

    - by Lirik
    Has anybody seen a GP implemented with online learning rather than the standard offline learning? I've done some stuff with genetic programs and I simply can't figure out what would be a good way to make the learning process online. Please let me know if you have any ideas, seen any implementations, or have any references that I can look at.

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  • Tooltips with infinite timeout?

    - by romkyns
    I'm thinking of setting the timeout on all my tooltips in a WinForms application to infinity (or an extremely large value). The motivation is that it's annoying for the user if the tooltip disappears while I'm still reading it, without providing any extra value whatsoever as far as I can tell. Normally I wouldn't ask something like this on StackOverflow, but the overwhelming majority of all software sets timeouts on tooltips, so it makes me wonder whether perhaps there is some important consideration I'm missing? Or is this just an old convention that nobody gives further thought to? If you would hate infinite timeout as opposed to a short timeout, please explain why. (If you just think tooltips are a bad idea altogether then that's a separate consideration; this question is specifically about the infinite timeout.)

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  • Encode complex number as RGB pixel

    - by Vi
    How is it better to encode a complex number into RGB pixel and vice versa? Probably (logarithm of) an absolute value goes to brightness and an argument goes to hue. Desaturated pixes should receive randomized argument in reverse transformation. Something like: 0 - (0,0,0) 1 - (255,0,0) -1 - (0,255,255) 0.5 - (128,0,0) i - (255,255,0) -i - (255,0,255) (0,0,0) - 0 (255,255,255) - e^(i * random) (128,128,128) - 0.5 * e^(i *random) (0,128,128) - -0.5 Are there ready-made formulas for that?

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  • Code Golf: Seven Segments

    - by LiraNuna
    The challenge The shortest code by character count to generate seven segment display representation of a given hex number. Input Input is made out of digits [0-9] and hex characters in both lower and upper case [a-fA-F] only. There is no need to handle special cases. Output Output will be the seven segment representation of the input, using those ASCII faces: _ _ _ _ _ _ _ _ _ _ _ _ | | | _| _| |_| |_ |_ | |_| |_| |_| |_ | _| |_ |_ |_| | |_ _| | _| |_| | |_| _| | | |_| |_ |_| |_ | Restrictions The use of the following is forbidden: eval, exec, system, figlet, toilet and external libraries. Test cases: Input: deadbeef Output: _ _ _ _ _ _||_ |_| _||_ |_ |_ |_ |_||_ | ||_||_||_ |_ | Input: 4F790D59 Output: _ _ _ _ _ _ |_||_ ||_|| | _||_ |_| || | _||_||_| _| _| Code count includes input/output (i.e full program).

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  • Algorithm to fill slots

    - by Peter Lang
    I am searching for an algorithm to fill several slots, which are already filled to some level. The current levels and the available quantity to fill are known Resulting levels should be as equal as possible, but existing level cannot be reduced Slots are filled from left to right, so left slots get higher level if equal level is impossible       The image above shows six examples, each column represents a slot. The grey area is already filled, the blue are is the expected position of the new elements. I could iterate through my slots and increase the quantity on the lowest slot by 1 until the available quantity is consumed, but I wonder about how to actually calculate the new filling levels. I am going to implement this with SQL/PL/SQL, other code is just as welcome though :)

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  • Regex & BBCode - Perfecting Nested Quote

    - by Moe
    Hey there, I'm working on some BBcode for my website. I've managed to get most of the codes working perfectly, however the [QUOTE] tag is giving me some grief. When I get something like this: [QUOTE=1] [QUOTE=2] This is a quote from someone else [/QUOTE] This is someone else quoting someone else [/QUOTE] It will return: > 1 said: [QUOTE=2]This is a quote from > someone else This is someone else quoting someone else[/QUOTE] So what is happening is the [/quote] from the nested quote is closing the quote block. The Regex I am using is: "[quote=(.*?)\](.*?)\[/quote\]'is" How can I make it so nested Quotes will appear properly? Thank you.

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  • New design patterns/design strategies

    - by steven
    I've studied and implemented design patterns for a few years now, and I'm wondering. What are some of the newer design patterns (since the GOF)? Also, what should one, similar to myself, study [in the way of software design] next? Note: I've been using TDD, and UML for some time now. I'm curious about the newer paradigm shifts, and or newer design patterns.

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  • Finite State Machine : Bad design?

    - by f4
    Are Finite State Machines generally considered as bad design in OOP ? I hear that a lot. And, after I had to work on a really old, undocumented piece of C++ making use of it, I tend to agree. It was a pain to debug. what about readability/maintainability concerns?

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  • Best graphical source code diff viewer/editor for code comparison and merging?

    - by Assaf Lavie
    The options for source code diff viewing/editing/merging seem to be: Free: Tortoise Merge Meld * WinDiff WinMerge * DiffMerge * KDiff AJC Diff Commercial: Total Commander's Diff viewer * Beyond Compare * Delta Walker * Araxis Merge * Are there any other options? (Wikipedia suggests a few) What's your favorite tools for source code diff? And how does it differ from the ones in the list? * Supports directory diffs

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  • What is instrumentation?

    - by Jon Seigel
    I've heard this term used a lot in the same context as logging, but I can't seem to find a clear definition of what it actually is. Is it simply a more general class of logging/monitoring tools and activities? Please provide sample code/scenarios when/how instrumentation should be used.

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  • Differences between Perl and PHP

    - by lok
    I'm planning to lern Perl 5 and as I have only used PHP until now, I wanted to know a bit about how the languages differ from each other. As PHP started out as a set of "Perl hacks" it has obviously cloned some of Perls features. What are the main differences in the syntax? Is it true that with Perl you have more options and ways to express something? Why is Perl not used for dynamic websites very often anymore? What made PHP gain more popularity than it?

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  • Building dictionary of words from large text

    - by LiorH
    I have a text file containing posts in English/Italian. I would like to read the posts into a data matrix so that each row represents a post and each column a word. The cells in the matrix are the counts of how many times each word appears in the post. The dictionary should consist of all the words in the whole file or a non exhaustive English/Italian dictionary. I know this is a common essential preprocessing step for NLP. Does anyone know of a tool\project that can perform this task? Someone mentioned apache lucene, do you know if lucene index can be serialized to a data-structure similar to my needs?

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  • Shut down windows service based on load

    - by JP
    Hello, I was wondering if there are any free / open source solutions that will start and stop a windows service based on load? I have some pubsub subscriber services that do background work which is not critical. Ideally i would like tot be able to automate things so that these services could start if memory/cpu/disk i/o was under a certain threshold and stop gracefully if that threshold was met. Do you know of any solutions? Thanks JP

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