Cuckoo hashing Cuckoo hashing example. The arrows show the alternative location of each key. A new item would be inserted in the location of A by moving A to its alternative location, currently occupied by B, and moving B to its alternative location which is currently vacant. Cuckoo hashing is a scheme in computer programming for resolving hash collisions of values of hash functions in a table, with worst-case constant lookup time. History[edit] Cuckoo hashing was first described by Rasmus Pagh and Flemming Friche Rodler in 2001.[1] Theory[edit] The basic idea is to use two hash functions instead of only one. When a new key is inserted, a greedy algorithm is used: The new key is inserted in one of its two possible locations, "kicking out", that is, displacing, any key that might already reside in this location. Lookup requires inspection of just two locations in the hash table, which takes constant time in the worst case (see Big O notation). Example[edit] The following hashfunctions are given:
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Blog » Blog Archive » In rainbows We get asked a lot about the colour-coding we give to places in Dopplr : what it represents, why we did it, how are the colours assigned. One of the main ‘atoms’ of Dopplr is unsurprisingly, place – so to make that run through the warp-and-weft of the user-interface, and our branding, was extremely important. The Dopplr logo, (or ‘SparkLogo’ * as we sometimes like to call it) is the clearest example of this perhaps. As you add trips to different destinations, Dopplr’s logo becomes your logo, reflecting what you’re doing – right the way through to the ‘ favicon ‘ that shows up in the address field of most browsers. It also makes for a great blog badge… As well as the aesthetic delights we believe that city colours bring to the service, we’re using them as visual ‘ affordances ‘ – ways to create implicit meaning and usefulness in the user-interface. We’re going to be doing far more with the city colours to create affordances in the near-future… But how do we generate them?
TIOBE Software: Tiobe Index TIOBE Index for January 2016 January Headline: Java is TIOBE's Programming Language of 2015! Java has won the TIOBE Index programming language award of the year. Java's rise goes hand in hand with Objective-C's decline (-5.88%). So what is the outlook for 2016? The TIOBE Programming Community index is an indicator of the popularity of programming languages. The index can be used to check whether your programming skills are still up to date or to make a strategic decision about what programming language should be adopted when starting to build a new software system. TIOBE Programming Community IndexSource: www.tiobe.com Java Python Visual Basic .NET JavaScript Assembly language Ruby Other programming languages The complete top 50 of programming languages is listed below. The Next 50 Programming Languages The following list of languages denotes #51 to #100. This Month's Changes in the Index This month the following changes have been made to the definition of the index: Very Long Term History
The Halton Sequence The Halton sequence can be used like a random number generator to produce points in the interval [0,1]. The Halton sequence is even less random than a random number generator; if you specify the index I of the Halton number you want, there is a formula for producing H(I). On the other hand, the Halton sequence does a better job of filling in the region, avoiding the large gaps that can occur with a random number generator. The idea is simple. and so on. How can we program this? The number I is input. To do this for base 3, just replace all the 2's by 3's. Now to get a "good" sequence of Halton points in 2D, we compute the X coordinates using a base of 2, and the Y coordinates using a base of 3. See if you can use this information, plus the text of the FORTRAN routine I_TO_HALTON_VECTOR, to produce a set of Halton points for 2D. Back to the Voronoi Project page.
PowerShell Tutorials PowerShell Tutorial for beginners. Windows PowerShell instruction thought-out for those new to PowerShell. In the next few weeks I will be posting a series of PowerShell basics that will provide a good start for a solid foundation. Here is what I have slated: The Windows PowerShell Console – Configuration and Customization.PowerShell Basics - Cmdlets, Parameters, Command Types, Command Information, etc…Output using the PowerShell Format command.Engaging the Windows File System.WMI and .NET primer (real basic)Variables in PowerShellTaking what you have learned and applying it. The initial lessons are concentrated around PowerShell as a Command Shell. Enjoy the Tutorials! Email This Page To A Friend
Stop using unsafe keyed hashes, use HMAC « root labs rdist The HMAC construction turns a cryptographic hash algorithm into a keyed hash. It is commonly used for integrity protection when the sender and recipient share a secret key. It was developed to address various problems with arbitrary keyed hash constructions. So why are developers still rolling their own? One of the original papers on keyed hash constructions describes the motivations for developing a standard for HMAC. The first construction the paper attacks is H(k || m), aka “secret prefix”. The second construction was H(m || k), aka “secret suffix”. The first attack is that secret suffix is weaker against offline second-preimage attacks. For a secure cryptographic hash function, a second-preimage attack takes 2n tries where n is the hash size in bits[1]. The other attack is much more powerful. This means the secret suffix construction is insecure if collisions can be found in the underlying hash function. MD5 has multiple demonstrated collisions.
exercism.io Exercism is all about having conversations about code. In order to start having those conversations, you need to install the exercism command line client. The exercism command line client is the all-in-one tool for fetching and submitting code. Let's get started. Software development is an activity that should not be performed in isolation. Exercism provides a launching point for this to occur. You fetch some challenges in the form of README documents. By repeating this process you will: Share while discussing how YOU solved the problem Learn from others as you discover how they solved the same problem Gain experience through repeated practice solving problems Don't be shy - start right now Begin by installing the exercism CLI (Command-Line Interface) tool. With the CLI installed, configure it using the configure command. Fetch your first problem by choosing a language from the languages tab above.
MIT’s Introduction to Algorithms, Lectures 7 and 8: Hashing - go This is the fifth post in an article series about MIT's lecture course "Introduction to Algorithms." In this post I will review lectures seven and eight, which are on the topic of Hashing. Many applications require a dynamic set that supports dictionary operations insert, search, and delete. For example, a compiler for a computer language maintains a symbol table, in which the keys of elements are arbitrary strings that correspond to identifiers in the language. A hash table is an effective data structure for implementing dictionaries. Lectures seven and eight cover various implementation techniques of hash tables and hash functions. Lecture 7: Hashing I Lecture seven starts with the symbol-table problem -- given a table S, we'd like to insert an element into S, delete an element from S and search for an element in S. The simplest solution to this problem is to use a direct-access (or direct-address) table. Using direct-address table, the dictionary operations are trivial to implement. PS.
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