Sumedh Meshram

A Personal Blog

NAVIGATION - SEARCH

An employee walked into my room today and said, "I want to Quit".

An employee walked into my room today and said, " I want to Quit".

I looked at him and asked for a reason.

 He said, " Culture in the office is too demotivating. People are gossiping and have no interest in their work. I think I am losing my skill set."

I smiled and said, "Fine!". But before you put down your papers, carry a glass full of water in your hand and take 3 rounds in the office making sure you don't spill even a single drop of water on the ground.

He was confused but agreed.

He came back after some time and kept the glass on the table. 

I asked him while you were taking rounds did you see anyone gossiping or did anyone disturb you.

He said NO. Rather I didn't notice because I wanted to make sure that water doesn't fall on the ground

So that is the point. If you are too focused on the job in hand, then external things won't disturb you at all.

So stay focused and keep working.

Success will come your way.

Thank you All

Thank you all, the Team of doctors @Dr. Ketan Chaturvedi @Dr. Suhas Salpekar @Dr. Tushar Pande and @Wockhardt hospital team (they stayed available 24X7) when I was under tremendous pain anytime and they show patience while treating an irascible person like me. A Special thanks to @Dr. Sushant Admane my chaddi buddy friend my brother from another mother who co-ordinates throughout the teams of doctors around the world so I can get the best possible treatments from such a unique health issue. Lastly, thanks to my family and friend who supported me as always to come out from this situation. Thanks Again to All... :) Stay Healthy 

TECHGIG : Code Contest HomeThe Great Indian Programming League 2013 - May Edition - Visit a Colony

Problem Statement :

In a colony all houses are in a single line. We call a house either in a good condition or in a bad condition. If a house is good its score is 1 otherwise 0. We decided to perform the scoring of houses in a different way. 

We not only consider that particular house but also the 2 neighboring house.
 
New scoring strategy- The Score of a house if affected by three house, that house and its two neighbors
 
Score-1 : If any of the three houses is in good condition 
Score-2 : if any of the two houses is in good condition 
Score-3 : if all the three houses are in good condition 
 
Now Josheph has the score list of all the houses ( according to new strategy ) and he wants to know what is the condition ( good or bad) of his house just seeing the score of the houses. He assumes that first house is in good condition.

MyResult

Successfully compiledSuccessfully compiled
: 9: 90
 
Solution :
using System;
public class CandidateCode
{
public static int house_condition(int[] input1,int input2)
{
int[] score = new int[input1.Length];	
for(int i=0;i<input1.Length;i++)
{
if(i == 0)
{
score[i] = 1; //first house in good condition

if(i+1<input1.Length)
{
score[i+1] = input1[i]- score[i];	
}
}
else
{
if(i+1<input1.Length)
{	
score[i+1] = input1[i] - (score[i-1] + score[i]);
}
}
}
return score[input2-1];	
}
}

The Partition Problem - Algorithm [Solved]

Partition Problem Problem

Partition problem is the task of deciding whether a given multiset of positive integers can be partitioned into two subsets S1 and S2 such that the sum of the elements in S1 equals the sum of the elements in S2.

using System;
using System.Linq;
public class CandidateCode
{
	public static string partition(int[] input1)
	{
		
		bool[] best_assignment = PartitionValues(input1);
		
		string result1 = "", result2 = "";
            	int total1 = 0, total2 = 0;
            	for (int i = 0; i < best_assignment.Length; i++)
            	{
	        	 if (best_assignment[i])
			 {
	    		   result1 += "\r\n " + input1[i];
	    		   total1 += input1[i];
			 }
			else
		         {
	         	   result2 += "\r\n " + input1[i];
	               	   total2 += input1[i];
		         }
		}
            if (result1.Length > 0) result1 = result1.Substring(2);
            if (result2.Length > 0) result2 = result2.Substring(2);

		return "{"+ result1 + " } {" + result2 + " } total  " + total1.ToString() + " & " + total2.ToString();
	}
	
	private static bool[] PartitionValues(int[] values)
	{
		bool[] best_assignment = new bool[values.Length];
            	bool[] test_assignment = new bool[values.Length];
            	
               	int total_value = values.Sum();

            	int best_err = total_value;
            	PartitionValuesFromIndex(values, 0, total_value, test_assignment, 0, ref best_assignment, ref best_err);
            
            	return best_assignment;
	}
	
private static void PartitionValuesFromIndex(int[] values, int start_index, int total_value,
            bool[] test_assignment, int test_value,
            ref bool[] best_assignment, ref int best_err)
        {
            // If start_index is beyond the end of the array,
            // then all entries have been assigned.
            if (start_index >= values.Length)
            {
                // We're done. See if this assignment is better than what we have so far.
                int test_err = Math.Abs(2 * test_value - total_value);
                if (test_err < best_err)
                {
                    // This is an improvement. Save it.
                    best_err = test_err;
                    best_assignment = (bool[])test_assignment.Clone();
                }
            }
            else
            {
                // Try adding values[start_index] to set 1.
                test_assignment[start_index] = true;
                PartitionValuesFromIndex(values, start_index + 1, total_value,
                    test_assignment, test_value + values[start_index],
                    ref best_assignment, ref best_err);

                // Try adding values[start_index] to set 2.
                test_assignment[start_index] = false;
                PartitionValuesFromIndex(values, start_index + 1, total_value,
                    test_assignment, test_value,
                    ref best_assignment, ref best_err);
            }
        }
}

Implementing Singleton in C#

Implementing Singleton in C#

Context

You are building an application in C#. You need a class that has only one instance, and you need to provide a global point of access to the instance. You want to be sure that your solution is efficient and that it takes advantage of the Microsoft .NET common language runtime features. You may also want to make sure that your solution is thread safe.

Implementation Strategy

Even though Singleton is a comparatively simple pattern, there are various tradeoffs and options, depending upon the implementation. The following is a series of implementation strategies with a discussion of their strengths and weaknesses.

Singleton

The following implementation of the Singleton design pattern follows the solution presented in Design Patterns: Elements of Reusable Object-Oriented Software [Gamma95] but modifies it to take advantage of language features available in C#, such as properties:

 

using System;

public class Singleton
{
   private static Singleton instance;

   private Singleton() {}

   public static Singleton Instance
   {
      get 
      {
         if (instance == null)
         {
            instance = new Singleton();
         }
         return instance;
      }
   }
}
 

This implementation has two main advantages:

  • Because the instance is created inside the Instance property method, the class can exercise additional functionality (for example, instantiating a subclass), even though it may introduce unwelcome dependencies.

  • The instantiation is not performed until an object asks for an instance; this approach is referred to as lazy instantiation. Lazy instantiation avoids instantiating unnecessary singletons when the application starts.

 

The main disadvantage of this implementation, however, is that it is not safe for multithreaded environments. If separate threads of execution enter the Instance property method at the same time, more that one instance of the Singleton object may be created. Each thread could execute the following statement and decide that a new instance has to be created:

if (instance == null)

Various approaches solve this problem. One approach is to use an idiom referred to as Double-Check Locking [Lea99]. However, C# in combination with the common language runtime provides a static initialization approach, which circumvents these issues without requiring the developer to explicitly code for thread safety.

Static Initialization

 

 

One of the reasons Design Patterns [Gamma95] avoided static initialization is because the C++ specification left some ambiguity around the initialization order of static variables. Fortunately, the .NET Framework resolves this ambiguity through its handling of variable initialization:

 

public sealed class Singleton
{
   private static readonly Singleton instance = new Singleton();
   
   private Singleton(){}

   public static Singleton Instance
   {
      get 
      {
         return instance; 
      }
   }
}
 

In this strategy, the instance is created the first time any member of the class is referenced. The common language runtime takes care of the variable initialization. The class is marked sealed to prevent derivation, which could add instances. For a discussion of the pros and cons of marking a class sealed, see [Sells03]. In addition, the variable is marked readonly, which means that it can be assigned only during static initialization (which is shown here) or in a class constructor.

This implementation is similar to the preceding example, except that it relies on the common language runtime to initialize the variable. It still addresses the two basic problems that the Singleton pattern is trying to solve: global access and instantiation control. The public static property provides a global access point to the instance. Also, because the constructor is private, the Singleton class cannot be instantiated outside of the class itself; therefore, the variable refers to the only instance that can exist in the system.

Because the Singleton instance is referenced by a private static member variable, the instantiation does not occur until the class is first referenced by a call to the Instanceproperty. This solution therefore implements a form of the lazy instantiation property, as in the Design Patterns form of Singleton.

The only potential downside of this approach is that you have less control over the mechanics of the instantiation. In the Design Patterns form, you were able to use a nondefault constructor or perform other tasks before the instantiation. Because the .NET Framework performs the initialization in this solution, you do not have these options. In most cases, static initialization is the preferred approach for implementing a Singleton in .NET.

Multithreaded Singleton

 

 

Static initialization is suitable for most situations. When your application must delay the instantiation, use a non-default constructor or perform other tasks before the instantiation, and work in a multithreaded environment, you need a different solution. Cases do exist, however, in which you cannot rely on the common language runtime to ensure thread safety, as in the Static Initialization example. In such cases, you must use specific language capabilities to ensure that only one instance of the object is created in the presence of multiple threads. One of the more common solutions is to use the Double-Check Locking [Lea99] idiom to keep separate threads from creating new instances of the singleton at the same time.

 

Note: The common language runtime resolves issues related to using Double-Check Locking that are common in other environments. For more information about these issues, see "The 'Double-Checked Locking Is Broken' Declaration," on the University of Maryland, Department of Computer Science Web site, athttp://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html.

 

The following implementation allows only a single thread to enter the critical area, which the lock block identifies, when no instance of Singleton has yet been created:

 

using System;

public sealed class Singleton
{
   private static volatile Singleton instance;
   private static object syncRoot = new Object();

   private Singleton() {}

   public static Singleton Instance
   {
      get 
      {
         if (instance == null) 
         {
            lock (syncRoot) 
            {
               if (instance == null) 
                  instance = new Singleton();
            }
         }

         return instance;
      }
   }
}
 

This approach ensures that only one instance is created and only when the instance is needed. Also, the variable is declared to be volatile to ensure that assignment to the instance variable completes before the instance variable can be accessed. Lastly, this approach uses a syncRoot instance to lock on, rather than locking on the type itself, to avoid deadlocks.

This double-check locking approach solves the thread concurrency problems while avoiding an exclusive lock in every call to the Instance property method. It also allows you to delay instantiation until the object is first accessed. In practice, an application rarely requires this type of implementation. In most cases, the static initialization approach is sufficient.

Resulting Context

Implementing Singleton in C# results in the following benefits and liabilities:

Benefits

 

  • The static initialization approach is possible because the .NET Framework explicitly defines how and when static variable initialization occurs.

  • The Double-Check Locking idiom described earlier in "Multithreaded Singleton" is implemented correctly in the common language runtime.

Liabilities

 

 

If your multithreaded application requires explicit initialization, you have to take precautions to avoid threading issues.

Acknowledgments

[Gamma95] Gamma, Helm, Johnson, and Vlissides. Design Patterns: Elements of Reusable Object-Oriented Software. Addison-Wesley, 1995.

[Lea99] Lea, Doug. Concurrent Programming in Java, Second Edition. Addison-Wesley, 1999.

[Sells03] Sells, Chris. "Sealed Sucks." sellsbrothers.com News. Available at: http://www.sellsbrothers.com/news/showTopic.aspx?ixTopic=411.

 

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