logic | 易学教程

number of possible sudoku puzzles [closed]

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问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed last year . Wiki http://en.wikipedia.org/wiki/Mathematics_of_Sudoku says Sudoku has 6,670,903,752,021,072,936,960 possible permutations.I tried to find out but it seems difficult.Can someone tell me how this number is calculated. 回答1: You can find all about it in this Wiki: http://en.wikipedia.org/wiki/Mathematics_of_Sudoku.

How to write reusable business logic in MVC models?

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问题 my problem is that we try to use a MVC (PHP) framework. After discussing a lot think that MVC is very good, but I'm missing the possibility to write reusable model-(application)logic. So, I'm not sure if we have the right approach to implement our software in a MVC framework. First I´ll describe the non-MVC, oo-approach which we use at the moment. For example - we are working on some browser games (yes that's our profession). Imagine we have an player object. We use this player object very

How can I manage a fork pool in Perl?

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问题 I'm setting something up to SSH out to several servers in 'batches'. I basically want to maintain 5 connections at a time, and when one finishes open up another (following an array of server IPs). I'm wondering for something like this should I be using fork()? If so, what logic can I use to ensure that the I maintain 5 children at a time? 回答1: Forking (or threading) is what you want, but you should look at CPAN for modules that will provide most of what you need to prevent you from

Correctness and Logic of algorithm: minimum steps to one

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问题 Problem Statement: On a positive integer, you can perform any one of the following 3 steps. Subtract 1 from it. ( n = n - 1 ) If its divisible by 2, divide by 2. ( if n % 2 == 0 , then n = n / 2 ) If its divisible by 3, divide by 3. ( if n % 3 == 0 , then n = n / 3 ) Given a positive integer n and you task is find the minimum number of steps that takes n to one . My Recursive Solution (in C++) compares all the 3 cases when N is divisible by 3, while the general solution compares only 2, but

Scala - Prefix Unary Operators

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问题 I've recently given Scala a second chance, and started with the project I always implement (in functional or pseudo-functional languages): an automated reasoner for propositional logic (and later predicate logic). Now, I've tried to get the notation of propositional logic in the language itself as pretty as possible, and I've gotten this far - with an implicit conversion (String -> Atom): ("A" and "B") implies "C" The functions "and" and "implies" (and "or" and "equivalent") are simple

Insert a row between two rows in SQL

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问题 I have a table like this, which shows which user commented on which parent thread. ParentID CommentID UserName CommentDateTime 58 58 Vicky 2016-12-02 11:51:07.270 58 61 Billu 2016-12-02 12:35:40.220 58 62 Rakesh 2016-12-02 12:37:42.133 If suppose a comment is made to the 2nd row, a new commentid is generated which is 63 I want to write a sql query which list the rows in the below order : ParentID CommentID UserName CommentDateTime 58 58 Vicky 2016-12-02 11:51:07.270 58 61 Billu 2016-12-02 12

Predictional Logic in Programming?

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问题 I was thinking about how in the probably distant future many people think that we wont rely on physical input (i.e. keyboard) as much because the technology that reads brain waves (which already exists to some extent) will be available. Kinda scares me....anyway, I while I was daydreaming about this, the idea came to me that: what if a programmer could implement logic in their code to accurately predict the users intentions and then carry out the intended operation with no need for human

R - vectorised conditional replace

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问题 Hi I'm trying manipulate a list of numbers and I would like to do so without a for loop, using fast native operation in R. The pseudocode for the manipulation is : By default the starting total is 100 (for every block within zeros) From the first zero to next zero, the moment the cumulative total falls by more than 2% replace all subsequent numbers with zero. Do this far all blocks of numbers within zeros The cumulative sums resets to 100 every time For example if following were my data : d <

Logic expression parser

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问题 I'm trying to create a logic expression parser for expressions like: ((VariableA -> VariableB) AND NOT VariableC) The parser should be able to return, whether the result is true or false for given values of variables. Basically, the expressions will only contain variables, logical operators (or, and, implication, equivalence, negation and parentheses). I would like to ask what is the best way to implement this kind of parser (using AST tree, or Reverse Polish Notation)? Or maybe there already

AI: Partial Unification in Open-World Reference Resolution

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When performing reference resolution on predicates describing the semantics of dialogue expressions, I need to be able to allow for partial unification due to working in an open world. For example, consider the following scenario: There is a blue box in front of you. We refer to this blue box using the id 3 . A set of predicates box(x)^blue(x) can easily resolve to the blue box you know about. Making this query will return 3 A set of predicates ball(x)^yellow(x) will not resolve to anything. This is fine. But now consider ball(x)^yellow(x)^box(y)^blue(y)^behind(x,y) that is, the yellow ball