Find first non-repeating character in String

Following code finds the first non-repeating character in just one pass :)


public class NonRepeating{

public static char firstNonRepeatingChar(String word)
{
Set<Character> repeating = new HashSet<Character>();
List<Character> nonRepeating = new ArrayList<Character>();

for (int i = 0; i < word.length(); i++)
{
char letter = word.charAt(i);
if (repeating.contains(letter))
{
continue;
}

if (nonRepeating.contains(letter))
{
nonRepeating.remove((Character) letter);
        repeating.add(letter);
}
else
{
nonRepeating.add(letter);
}
}

if(nonRepeating.size()!=0)
 return nonRepeating.get(0);
else
  return '\0';
}


public static void main(String[] args)
{
char ans = firstNonRepeatingChar("hrishikesh");

System.out.println("ans="+ans);
}
}

Fibonacci Series

Fibonacci Series = 0 1 1 2 3 5 8 13 21 34.

Basically we have to add the previous and current number to get the next number.


Java Code->
public class Fibonacci
{
    static int[] fibonacci(int n)
    {
     //Declare an array to store Fibonacci numbers
     int f[] = new int[n+1];
     int i;
   
     //0th and 1st number of the series are 0 and 1
     f[0] = 0;
     f[1] = 1;
   
     for (i = 2; i <= n; i++)
     {
    //Add the previous 2 numbers in the series and store it
        f[i] = f[i-1] + f[i-2];
     }
   
      return f; //Return the array back to main method.
    }

 
   public static void main(String[] args)
   {
     int n = 9;
     int[] ans = fibonacci(n);
 
     for (int i = 0; i <= n; i++)
     {
        System.out.print(ans[i]+" "); //Print the array.
     }
   }

}

Pair Programming

In Pair Programming two programmers work together on the same computer.

One person writes the code while the other reviews it. They also switch their roles frequently.

Both have to maintain a running commentary, basically they have to "program out loud".

Multiple configuration files

Hibernate is designed to be used with a large set of databases. The details of those databases are configured in an XML file called hibernate.cfg.xml.

If we wish to use multiple databases in our application then we have to maintain separate configuration files.


Example: Application uses Oracle and Derby database.

Here we have to maintain 2 configuration files, lets say we name it oracleconfig.cfg.xml and derbyconfig.cfg.xml.

To access them we need to create separate session Factories ->

1) SessionFactory sessionFactory1 = new  Configuration().configure("oracleconfig.cfg.xml").buildSessionFactory();

2) SessionFactory sessionFactory2 = new Configuration().configure("derbyconfig.cfg.xml").buildSessionFactory();

Space Complexity

Usually the term Space Complexity is misused for Auxiliary Space.

Following are the correct definitions of Auxiliary Space and Space Complexity.

Auxiliary Space is the temporary space used by an algorithm.

Space Complexity of an algorithm is total space taken by the algorithm with respect to the input size.

Space complexity includes both Auxiliary space and space used by input.

Example:
While comparing sorting algorithms on the basis of space, Auxiliary Space would be a better choice than Space Complexity.