Novel finder Program

This was one of the problems that I had faced during one of my interviews. The problem sounded interesting and I was given 1 hour to solve it which I did quite comfortably.

Problem:

The K-doublets of a string of characters are the ordered pairs of characters that are K distance from each other. A string is K-singular if all its K- doublets are different. A string is Novel String if it is K-singular for all possible K distances.

For e.g. take the string FLBL, its 0-doublets are FL, LB and BL. Since all these are different, FLBL is 0-singular. Similarly, its 1-doublets are FB and LL, since they are different FLBL is 1-singular as well. Lastly, the only 2-doublet of FLBL is FL, so FLBL is 2-singular. Hence, FLBL is a Novel String.

Note that the fact that FL is both a 0-doublet and 2-doublet is insignificant as zero and two are different distances.

Input:

The input is one or more non-empty strings of at most 100 capital letters, each string on a line by itself, followed by a line containing only two dollars ($$) signaling the end of the input.

Output:

For each input line, output whether or not it is a Novel string using the exact output format shown below.

Sample Input: (Input File: novel.in)

FLBL

FFLL

ORDINARY

R

QYQRQYY

$$

Sample Output: (Output File: novel.out)

FLBL is a Novel string

FFLL is not a Novel string

ORDINARY is a Novel string

R is a Novel string

QYQRQYY is not a Novel string

Solution:

QTo attack this problem, you first have to find all the doublets for each distance starting from 0 to the maximum distance which would string's length minus one. Then keep pushing them into a hash set. Whenever the add() method of the Set returns false, it means we are adding a duplicate hence, its not a Novel text. Here is the Java source code.

import java.io.*;
import java.util.*;

public class NovelFinder {
 public static void main(String[] args) throws Exception {
  File inputFile = new File("novel.in");
  Scanner scanner = new Scanner(inputFile);
  BufferedWriter out  = new BufferedWriter(new FileWriter("novel.out"));
        NovelFinder finder = new NovelFinder();
        while (scanner.hasNextLine()) 
            out.write( finder.find(scanner.nextLine()) + "\n");                
        out.close();
 }
 
 public String find(String inString){
  for(int j=1;j<inString.length();j++){
   Set<String> checkerHash = new HashSet<String>();
   for(int i=0;i+j < inString.length();i++)
    if (!checkerHash.add(inString.charAt(i) + "" + inString.charAt(i + j)))
     return inString + " is not a Novel string";
  }
  return inString + " is a Novel string";
 }
}

Cheers!
Braga

Windows Phone 7.5 - Home button Navigation and Exit Confirmation

While developing a windows phone application, the one which involves navigation to various pages starting from something called as a homepage would quickly become annoying. You will find yourself in deeper pages and as a means on coming back to the home page, you will keep pressing the back button so many times it will exit you out of the application.

There are couple of problems associated with this. The user is forced to keep in mind how deep he has in the navigation page. The other main problem is he will not have patience to wait to go to the home page and pressing the back button on the first page will obviously throw you. This is because the navigation details are stored in a stack.

It is always nice to provide a home button to the end user on all the pages so that on click of them will take it to the home. Also, you can always have a confirmation dialogue fired while exiting the application. First problem first.

This code armed with a Home button will do the job cleanly for you.

private void Home_Click(object sender, System.Windows.RoutedEventArgs e)
{
    int depth = NavigationService.BackStack.Count();
    for (int i = 0; i < depth - 1; i++) { NavigationService.RemoveBackEntry(); }
    NavigationService.GoBack();
}

The funda here is it will empty all the stack and will call the back action of the navigation service just once making sure that the next back() will empty the stack and will make you quit.

As I told before adding this code to the MainPage.xaml.cs will show a confirmation popup while quitting the application so that user only deliberately quits but not accidentally.

protected override void OnBackKeyPress(System.ComponentModel.CancelEventArgs e)
{
    if (MessageBox.Show("Are you sure you want to exit?", "Exit?", MessageBoxButton.OKCancel) != MessageBoxResult.OK)
    {
        e.Cancel = true;
    }
}

These techniques are very simple and subtle but will improve the usability of your application by leaps and bounds.

Cheers!
Braga

Windows Phone 7.5 WebBrowserTask - Simple Yet Powerful

WebBrowserTask is one of the most simple yet powerful tasks I found in Windows Mobile development. It is amazingly simple, just two or three lines of code and super tempting to include it in your project. Lets quickly see how to use it and places where you can utilize its capability at the presentation level.

Enough intro, here is the code

WebBrowserTask pptTask = new WebBrowserTask();
pptTask.Uri = new Uri("http://www.iasted.org/conferences/formatting/presentations-tips.ppt");
pptTask.Show();

Damn simple isnt it? You could use this in places where you need to launch or open an URL in the inbuilt Internet Explorer. And the best thing about this is it will automatically detect the attachment file types (most of them) and opens them cleanly. For example, it could read ppt, pdf, xls even videos and open them cleanly. You can make the integration look rich by providing a button in the Application bar. Following is a screenshot.

Besides opening simple URLs consider using this Task to open regular attachments and make your end application look extremely rich with just one or two lines of code.

Cheers!

Braga