C#

Single-line Solution: Fibonacci number

Max Paulousky — Fri, 26 Feb 2010 21:45:28 GMT

As I mention in my previous post, next single-line function to implement is Fibonacci number.

By definition, the first two Fibonacci numbers are 0 and 1, and each remaining number is the sum of the previous two. Some sources omit the initial 0, instead beginning the sequence with two 1s. (by Wikipedia)

There are some variants to calculate Fibonacci number. First one is recursion:

     Func<int, int> fib = null; 

    fib = n => (n < 2) ? 1 : fib(n-1) + fib(n-2);

As I show in the previous post, this code can’t be a solution (nonsingle-line code). By the way, this code is absolutely inefficient. It has order of O(φⁿ) time complexity.

Next algorithm is computing Fibonacci number via its matrix representation. This algorithm is very efficient (order of O(log₂n) time complexity) but has great number of calculations (additions, multiplications, exponentiations). It will be difficult to understand such an implementation.

The best approach is the third variant. It is efficient enough O(n) and has just two operation. The algorithm can be written as

    Fib2(n):

         i := 1

         j := 1

         for k := 3 to n do

            j := i+j

            i := j-i

         return j

This code can be implemented in C# 3.5, Linq as

    int fib = Enumerable.Range(1, n).Skip(2).Aggregate(new KeyValuePair<int, int>(1, 1), (seq, index) => new KeyValuePair<int, int>(seq.Value, seq.Key + seq.Value)).Value;

Yes, it is quite long but it works!

I create a range from 1 to n; skip first two elements (we know they values); store initial values in the KeyValuePair instance (1 and 1). In the aggregator function I repeat calculations as in the loop above.

Can anyone implement the same functions using other programming languages and the single-line approach?

Great discussion of Fibonacci numbers calculation using various programming languages is here.

That is it!

Tagged: C# , Recursion , Single-Line Code , Linq , Fibonacci

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Single-Line Solution: Factorial

Max Paulousky — Thu, 25 Feb 2010 21:09:26 GMT

Recently my colleagues started a dispute whether it is possible to calculate a factorial using just one line of code.

In mathematics, the factorial of a non-negative integer n, denoted by n!, is the product of all positive integers less than or equal to n. (by Wikipedia)

One line means a line that ends with a semicolon:

     bla-bla-bla;

Of course, following sample is not the single-row code:

    for(;;;) bla-bla-bla;

First idea is using recursion (let’s arrange, it is the single-line code):

    Func<int, int> factorial = n => n < 2 ? 1 : n * factorial(n - 1);

    int result = factorial(10);

but it does not work (the factorial expression is not defined before evaluating the right side of the assignment).

Following variant works but it is not the single-row solution (at least two code lines – factorial defining and initializing):

    Func<int, int> factorial = null; 

    factorial = n => n < 2 ? 1 : n * factorial(n - 1);

    int result = factorial(10);

The simplest variant of the single-line factorial calculating is

    int factorial = Enumerable.Range(1, n).Aggregate((accumulator, next) => accumulator * next);

The aggregate function takes the first element of the enumeration and put it into accumulator. Then it multiplies accumulator and next and put the result into accumulator again. Aggregate repeats the action for all elements. The result looks like

    (....((((1 * 2) * 3) * 4) * 5) * .......) * n

Next single-line solution I want to implement is a Fibonacci calculator.

Tagged: c# , Factorial , Recursion , Signle-Line Code , Linq , Fibonacci

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How to get Xml InnerText in a Silverlight application – 2

Max Paulousky — Mon, 15 Feb 2010 19:40:05 GMT

There is an easier way to remove all xml tags from the document – regular expressions:

     Regex.Replace(text, @"<\/?[^>]*\/?>", string.Empty); 

Tagged: Silverlight , Xml , InnerText , Regular Expressions

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How to get Xml InnerText in a Silverlight application

Max Paulousky — Sat, 30 Jan 2010 13:07:37 GMT

The Silverlight framework is restricted in comparison with .Net framework. It does not provide the XmlDocument class, that has the InnerText property. Silverlight applications should use XDocument instead of XmlDocument. Following code is an extension method for the XNode class that implements InnerText functionality.

     public static string InnerText(this XNode xNode)

    {

      bool isContainer = xNode is XContainer;

      if (!isContainer)

      {

        switch (xNode.NodeType)

        {

          case XmlNodeType.Text:

          case XmlNodeType.CDATA:

          case XmlNodeType.Whitespace:

          case XmlNodeType.SignificantWhitespace:

            return xNode.ToString();

          default:

            return string.Empty;

        }

      }

      else

      {

        XContainer xContainer = (XContainer)xNode;

        StringBuilder sb = new StringBuilder();

        for (XNode node = xContainer.FirstNode; node != null; node = node.NextNode)

          sb.Append(node.InnerText());

        return sb.ToString();

      }

    }

XContainer is a type of xml nodes that contain child nodes and they should be processed recursively.

Tagged: Silverlight , Xml , XDocument , XNode , InnerText

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