Tuesday, May 24, 2016

Getting MotoG active display without Root

Hey guys, I am starting a new series of introducing some of the very cool apps of Android.

Today I am going to an app that will emulate MotoG Active Display feature. The app is ACDisplay.

Here are steps to install ACDisplay and make it look alike Active Display.
  1. Install it using the play store, link.
  2. After installation open it.

  3. Clicking the yellow mark will tell you what all permissions you have to give AcDisplay.

  4. Give all the permissions to it, namely Device Administrators and Notification Access.

  5. Device Administrators is required to lock the Device and Notification Access is required so that you can read all the notifications(although you can configure it, which Apps you don't need).
  6. You are almost done (yellow mark is also gone), after you give the permissions your basic setup is ready to use.
  7. Enable the global button on the top right hand corner.

  8. This will enable the app. Now lets change some config. 
  9. Settings will have 2 sections:
    1. Features
      1. LockScreen
        1. Go to this and enable it on the top right hand corner, this will make this as the lock screen
        2. Check Enable when no notifications if you want to show it irrespective of whether there are 0 notifications or more than that.
      2. Active Mode
        1. Go to this and enable it on top right hand corner, this will give you options for the behavior of the AcDisplay, wave to wake, disable on low battery etc.
    2. Settings
      1. Notifications
        1. This will give you the option what to do with the notification, like wake up or not on arrrival of new notification, to show always on notifications or not etc.
      2. Interface
        1. This will give you the option to use the desktop wallpaper as background for this lock screen, animation, colors etc.
      3. Apps
        1. This will be useful to blacklisting the app, that means app which you don't want to show the notifications for.
      4. More
        1. This gives you the option when to make this app active, only on charging or everytime, inactive hours (for which app will be in sleep), shortcuts like lower left hand shortcut, lower right hand shortcut etc.
  10. After then when you lock the device and wake it up, AcDisplay will spread its magic, but the main problem is that it just disappears if you press the home button, and comes to home screen, so in order to solve that we will pattern protect our phone via default locker. 
  11. For that go to Settings->Lock Screen->Screen Lock->Pattern and give the pattern, confirm it.
  12. Enable :
    1. Directly Show pattern view, 
    2. make pattern visible
    3. show pattern error
    4. show pattern dots
  13. Set automatically lock to immediately, enable power button instantly locks
  14. At last we will disable notifications in lock screen, since our notifications will come at AcDisplay, for that Settings->Notifications->When device is locked->Don't show notifications at all
  15. Now lock the screen, and whenever notification come, depending on the wake up setting of the AcDisplay, mobile will lighten up, and show the notification very similar to the Moto Active Display, tap the small icon and read the notification, tapping after selecting the notification will take you to the app itself, but before that you have to give correct pattern.


  1. The AcDisplay best works with default lockscreen, do not use with other lock screens.
  2. Don't forget to set the pattern or pin or password lock for default lock since pressing the menu button bypasses the screen.
  3. It acts as a module of Xposed as well, which is an optional setting, you can enable it in Xposed Module, modules section, if your xposed module is setup, that means both rooted and xposed installed and configured.

Monday, May 16, 2016

Remove duplicates from sorted array.

There are a number of approaches when it comes to remove the duplicates, from the array. Here are some of them:

  1. Make a Set out of the array so that you have only the unique elements out of it, also considering the further point if you want to keep track of the order of the elements you can use LinkedHashSet that guarantees the uniqueness as well as order of the Collection.
  2. Next approach is bit granular and we traverse the array and keeps on pushing the pointers till I am getting the same element:
    1. Start with 2 pointers first marked at 0 (since it is an array, lets name it as f) and second marked at 1(lets name it as s).
    2. Keep incrementing the second pointer till the elements at ARRAY[f] and ARRAY[s] are equal.
    3. When above condition is false make ARRAY[f] = ARRAY[s] and increment both f and s since the position of f and s are traversed.
Coming to the implementation, here is the working code.

This is the code you can find the running code here.

import java.util.*;
import java.lang.*;
import java.io.*;
class Ideone
      public static int[] duplicatesRemoval(int[] input){
        int f = 0;
        int s = 1;
        if(input.length < 2){
            return input;
        while(s < input.length){
            if(input[s] == input[f]){
             **THIS PART CAN BE SHORTENED BY input[++f] = input[s++];
                input[f] = input[s];
        //reassigning to new array element
        int[] result = new int[f+1];
        for(int k=0; k<result.length; k++){
            result[k] = input[k];
        return result;
    public static void main(String a[]){
        int[] input = {2,3,6,6,8,9,10,10,10,12,12};
        int[] output = duplicatesRemoval(input);
        for(int i:output){
            System.out.print(i+" ");

Wednesday, May 11, 2016

Next greater number with same set of digits

This is pretty interesting question I came across when facing an interview.

The question was pretty straight forward, you have given a number and you have to find the next greater number with the same set of digits as in the given number. So for an instance if Number is:
  1. 1234 then output should be 1243
  2. 4321 then output should be not possible since its the largest among all the possible numbers with the same digits as in 1234
  3. For other cases we have to develop the algorithm (:D).
Now coming to the solution of this problem, one straight forward algorithm would be:
  1. Find all the possible combination of the string (given number) and collect it in a Sortable Collection like TreeSet and take the next element after the given number. This is pretty straight forward approach but it is waste since we have to calculate the full set of numbers that are possible to get generated and then find the next number in the TreeSet. This is simple to understand but memory wise, order wise and space wise pretty heavy.
    Although I have given this answer only :D, but the interviewer was happy with it at all. Since there are better approaches to this.
  2. Next approach is pretty simple but a bit difficult to understand. Here it goes:
    1. First 2 condition will be same as the ascending and descending one.
    2. If the case is different then we will :
      1. take pair of digits from right where right digit is greater then left digit, and mark the index to be right digit index - 1.
      2. Then we have to take the smallest digit from the right hand side digits of the marked index which is greater then the indexed digit
      3. Then sort the right side of the index digit in ascending order.
      4. What, what what :D
    3. Lets take an example: 54362
      1. In this example start from the right in pair, (2,6) [we will ignore since 2<6] and move to next pair that is (6,3). This is correct pair since 6>3.
      2. So our marking index would be 2 and the number to be updated is 3.
      3. Now taking the number which appears in right side of index number(ie 2) and is smallest among them but larger then 3.
      4. In this case it is 6 only since 2 is smallest but 2>3 is false.
      5. So we swap 3 and 6 which will make the number as 54632 and sort the right hand of index(2) that means numbers 3,2 have to be sorted which is true in this case.
Lets make the program of this. Here it goes:

import java.util.Arrays;

 * @author ankur
public class MyData {

 private int n;
 private int nAsc;
 private int nDesc;
 private int[] nIntArr;
 private int length;
 private String sAsc;
 private String sDesc;
 public MyData(int n){
  this.n = n;
 private void process(){
  String s = "" + this.n;
  char [] sArr = s.toCharArray();
  nIntArr = new int[sArr.length];
  for(int i=0, len=sArr.length; i<len; i++){
   nIntArr[i] = Integer.parseInt("" + sArr[i]);
  sAsc =  new String(sArr);
  sDesc = new StringBuffer(sAsc).reverse().toString();
  nAsc = Integer.parseInt(sAsc);
  nDesc = Integer.parseInt(sDesc);
  length = this.sAsc.length();
 public int getN() {
  return n;
 public void setN(int n) {
  this.n = n;

 public int getnAsc() {
  return nAsc;

 public void setnAsc(int nAsc) {
  this.nAsc = nAsc;

 public int getnDesc() {
  return nDesc;

 public void setnDesc(int nDesc) {
  this.nDesc = nDesc;

 public String getsAsc() {
  return sAsc;

 public void setsAsc(String sAsc) {
  this.sAsc = sAsc;

 public String getsDesc() {
  return sDesc;

 public void setsDesc(String sDesc) {
  this.sDesc = sDesc;

 public int[] getnIntArr() {
  return nIntArr;

 public void setnIntArr(int[] nIntArr) {
  this.nIntArr = nIntArr;

 public int getLength() {
  return length;

 public void setLength(int length) {
  this.length = length;

package com.av.ngnsd;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Main {

 public static void main(String[] args) {
  MyData myData = new MyData(54362);
   int nextNum = process(myData);
   System.out.println("Next number is " + nextNum);
  }catch(Exception ex){
 public static int process(final MyData n) throws Exception{
  int result = 0;
  int nDesc = n.getnDesc();
  int nAsc = n.getnAsc();
  if(nDesc == n.getN()){
   throw new Exception("Not possible");
  }else if(nAsc == n.getN()){
   String s = "" + nAsc;
   result = Integer.parseInt(s.substring(0, s.length()-2) + "" + s.charAt(s.length()-1) + s.charAt(s.length()-2));  
   //TODO the main code
   int []nCharArr = n.getnIntArr();
   int indexOfChange = -1;
   for(int i=n.getLength()-1; i>0; i--){
     indexOfChange = i;
   if(indexOfChange <= 0){
    throw new Exception("Not possible");
    int numberToBeSwapped = nCharArr[indexOfChange-1], smallestIndex = indexOfChange;
    //getting the smallest among the right side of the index which is greater then index digit
    for(int i=indexOfChange+1; i<n.getLength(); i++){
     if(numberToBeSwapped < nCharArr[i] && nCharArr[i] < nCharArr[smallestIndex] ){
      smallestIndex = i;
    //swapping the 2 digits
    int temp = numberToBeSwapped;
    nCharArr[indexOfChange-1] = nCharArr[smallestIndex];
    nCharArr[smallestIndex] = temp;
    //for sorting the right hand side of the index
    List<Integer> nArrayList = new ArrayList<Integer>();
    for(int i=indexOfChange+1; i<n.getLength(); i++){
    //int indexOfChangeCopy = indexOfChange;
    for(int num:nArrayList){
     nCharArr[++indexOfChange] = num;
    StringBuilder strNum = new StringBuilder();
    for (int num : nCharArr) 
    result = Integer.parseInt(strNum.toString());
  return result;

Sunday, April 17, 2016

Installing gnome and enabling all windows in top bar

Ubuntu comes with the default launcher as Unity Launcher that looks like this:

Now this launcher is pretty but if you want the Gnome desktop you can continue or else press the (X) button :D .
  1. For installing the Gnome desktop, we first install tasksel, that is pretty useful in order to install many packages.
  2. For that go to Ubuntu Software Center and type tasksel
  3. Install the package and run using sudo tasksel 
  4. Pressing arrows you can navigate and pressing space bar can check/uncheck the package
  5. Go to Ubuntu Gnome desktop and press space bar to select it and pressing tab will take you to ok at the bottom.
  6. Press space bar being at OK
  7. Wait till the package is installed and after that restart the system using either command or either via UI.
  8. When you restart the system you will find out that now your desktop is changed to Gnome.
Now the problem with gnome (or feature) is that it only shows the active window in the top bar and not all the windows that are opened. In this pic although there are 3 windows opened but only one is showing in the top bar in left corner which is active one:

In order to do get all the windows we have to install the extension and enable it to work with GNOME desktop.

Extensions are very useful in extending the functionality of the Gnome desktop. 

The extension we need for showing all the opened windows in the top bar is YAWL, which you can get here
  1. sudo apt-get install gnome-common autoconf autogen automake intltool libglib2.0-dev
  2. cd /path/to/where/you/want/subdir/with/yawl
  3. git clone https://github.com/dbfin/gnome-shell-extension-yawl
  4. cd gnome-shell-extension-yawl
  5. ./install-extension yawl
Once this is done, this means that you have installed the extension but till now didn't enabled it. For enabling the extension we have to install the gnome-tweak-tool, which is capable of tweaking the settings of Gnome desktop. For installing gnome-tweak-tool use:
  1. sudo apt-get install unity-tweak-tool gnome-tweak-tool
Once this is done you can start it using sudo gnome-tweak-tool .
Go to extensions, scroll to Yawl and enable it once that is enabled you have all the windows and favorites available at the top bar

This will give you all the opened windows at the top bar including the favorites.

Also in some cases you might see the message that the extension is not compatible with shell version, this is because as the shell is updated their might be the chance that extension might not support that change in that cases we have to switch off the default feature of the gnome that checks for the compatibility of the extension by the command:

gsettings set org.gnome.shell disable-extension-version-validation "true"

Phew this was a pain in my case since I have actually searched a lot in order to all these things. Hope this helped you all :) .

Creating a node module and using it

As you all knows, Node is getting better day by day and also there is an option of using node modules that are generated by other developers and are available to use.

Also, there is no good in making a Node project without user defined modules or in other words I can say that there is not possible (all though you can create a single module project but that is of no use) to generate the project in which you do not create the modules.

So, going forward Node modules are just the way of exposing a functionality from a Node file so that you can use that in other functions. For instance you want to create a calculator in Node js and for that you have decided that there would be four different modules namely add, subtract, division and multiply so that you can control them very gracefully and also tracing bugs would be easy since there are individual modules so when the bug got traced you can easily go to specific module in order to debug it.

So in order to do that, follow the steps:
  1. lets create a folder named node-calculator, for that browse to your docs and create a new folder either through right click and new folder or from shell using
    $ mkdir node-calculator 
  2. Go inside the folder using cd node-calculator and create one more directory named my_modules using :
    $ mkdir my_modules
  3. Now our basic setup is ready so we will code the things.
  4. Let us first create a module named add. 
  5. For that we will create a directory inside my_modules named add
  6. We will create a file inside add folder named index.js with following contents:
    var addition = function(a,b){
      return a+b;
    module.exports = {
      addition_two_numbers  : addition 
  7. In this the function addition is pretty simple and in order to expose that function to be useful in other files we have exported it with the name, addition_two_numbers
  8. Now create a file in node_calculator directory named calc.js with following contents:
    var add_module = require("./my_modules/add");
    console.log("Add module ", add_module.addition_two_numbers(2,2));
  9. Similarly create other modules named div, sub and mul. 
  10. Now the tree node-calculator command to see the contents and you will see something like this :
For your information:
  1. Code is available here
  2. The output shown at step 10 is of the command tree node_calculator
  3. If you don't have the tree command you can get it by:
    apt-get install tree
  4. In order to run the file use the node filename.js .
So for us it would be node calc.js and you will get the answer 4.

Saturday, April 16, 2016

Wifi router speed issues and solutions

I have been working lately in my laptop (while connected to wifi) and suddenly the internet becomes very slow. I have tested the speed of internet using the www.speedtest.net. The result of speedtest was awesome and I thought it might be the case with my laptop since it is running from 2 days (not continuously, uses hibernates when need to stop working, ;) ) let us restart the machine and then will look again on the issue. But surprisingly the issue didn't solved, then I called the ISP provider call center and have scheduled a time for next day when their engineer might come and look in to the issue.

Okay, next day the engineer came and before saying anything he took my laptop and used some of the commands like:
  • ping google.com
  • ping youtube.com
to see that the net is working or not. He shown me the result saying sir there is no loss in the packets.

I was also confused how this is possible I am unable to play a single youtube video without buffering even when my internet speed package is 40 mbps plan which is pretty descent to run youtube videos in HD.

Then I started searching the internet that what is the issue and came to know that since Wifi is a machine that works in radio waves, there may be chances that other systems might be interfering in the signals of the router and so you might face some of the issues. The solutions are pretty simple and here are some of them what I got from internet.
  1. Don't place the router near to TV, Sound Systems, Microwaves or anything that is capable of creating the Radio waves and might be responsible to interfere in the signals of your router.
  2. Place the router somewhere at top, since it is tested that the signals never broadcast parallel to the position of router rather they actually circulate and go down after some distance so if you place the router at some where which is at more height than it might be the case that you can get better connectivity at the corners of your house.
  3. Check the interference of the signals with the help of an Android program named Wifi Analyser that analyses all the wifi signals in both the bands (2.4ghz, 5ghz) under all channels, and then decide which channel is best suited for your router to work properly. The output of the wifi analyser is somewhat looks like this:

    Now this is pretty confusing but let me give you a brief explanation that this is actually showing all the wifi signals that you are receiving in your area and all the channels under which the wifi routers are broadcasting their signals. Most of the wifi routers work at the auto mode of channels so this application tells you which signal is best for your router to work so that you can change the settings of your router from the settings page that you can get at
I actually did all these and the problem never gets solved. At last I came to know that the solution of these situations are either you gets shifted to places where there is less congestion that is next to impossible or you have to change your router, this means change the router and get the one that has high frequency meaning 5 ghz. Since my router works on 2.4 ghz and there are too many routers that are working in the same frequency I am getting the issues but if you change your router there are very chances that you might get the interference since very few people takes 5 ghz router. 

So for all of you, you can follow some of the above steps to get the problem solved or either get the new router with 5 ghz frequency, their might be the case that you can get the same problem in 5 ghz router as well but chances are very low.

Hope you guys enjoyed my info, sorry but there is no solution I got that worked for me, that's why I have given the solution which is not that feasible but its ok :)

Wednesday, April 6, 2016

Callback hell and promises

Callback? What the hell is callback? Well in a nutshell, call back means:

Now this is what just the English meaning of call back. This in turn means executing something when other thing is finished and this in turn is not something that keeps on waiting for the thing to finish, rather keeps on doing its other stuff and executes when the thing is finished on an event basis.

1. What is callback?

The statement above is a bit lengthy in a way to understand, but think of this that when you give exams in school you never waits for the result( although you do :D ), rather you start preparing for the next class and when the result arrives, go to school to collect it. So if we have to think this in a code manner it would look something like this:

     //when results arrive

This pattern is very common in Javascript world. If you ever been worked with Javascript in client side ( or server side, since Node js made that possible ) you would have faced the situation when you have to get some data from the server without doing the full reload of the page using ajax call and then have to display the result on the page at some specific div or text area.

This can be done using callback in Javascript like this:

     url : "", //where to hit

     type : "POST",//how to hit, POST, GET, DELETE, PUT
     data : {},//what to send
     success : function(resposne){//in case of success
          //this executes when call gets successful and we have the response in the response object of the function paramter

     error : function(error){//in case of failure
          //this executes when call faces some error


FYI : The call above uses Jquery framework to call the ajax function.

The function named success and error are nothing but the callbacks, since they are going to be called once the main call comes back either with the failure or with the success status.

2. What is callback hell?

The way callback is handled a pretty different then most of the other languages handle the stuff. For instance in Java:
public static void sleepAndPrint() throws Exception{
     System.out.println("I am before sleep");
     System.out.println("I am after sleep");

Calling the above function will provide you the output as:

I am before sleep. (There will be a pause of 2 seconds and then next statement occurs)
I an after sleep.

Now considering the same and making it in Javascript we have something like this:
function sleepAndPrint(){
     console.log("I am before timeout");
          console.log("I am in timeout");
     }, 2000);
     console.log("I am after timeout");

Now when you run this you will get some thing like this:

I am before timeout.
I am after timeout.
I am in timeout.

If you see at the time of timeout function the code didn't stopped and keeps on executing so the statement that was inside the timeout block actually got executed after the whole program gets done.

This is good in a way that Javascript actually follows Non-Blocking I/O model, but it also creates a problem for those who wants to do the stuff in a sequential basis, like you want to get the data of a user from the database, that will contain the github id of the user from which you can query the github servers using the github api and get the avatar url of the user so that you can download it in a temporary folder. Now the above mentioned sequence is a straight forward one if we have to do it in Java like this:
public User getData(final int userId) {
     //this will be having the code to access the db layer and get the User model out of it
     return user;

public String getUserAvatarUrlFromUser(final int userId){
     User user = getData(userId);
     String avatarUrl = user.getAvatarUrl();
     return avatarUrl;

public Image getImageFromGihubForAvatarUrl(final int userId){
     String avatarUrl = getUserAvatarUrlFromUser(userId);
     Image image = github call to get the image of the avatar url just found;
     return image;
//Some where in the code

This will go on the way we have planned and the code when talking to database actually waits for the operation to complete and in the same way while talking to the github servers actually waits which makes our program to run in sequence and thus does not make any problem for us.

But in case of Javascript since the default behavior is different this sequence is not going to work properly.

So we have to do work like this, not exactly but something like this:
var getUserAvatarWithCallback = function(userId, callback){
  db.getUsers("userId", function(error, response){
    if(error){callback(error, null);}
      var userIdOfGh = response.user.githubId;
      github.search.users({ q : userIdOfGh }, function(err, res){
        if(err){ callback(err, null); }
          var avatarUrl = res.items[0].avatar_url;
          callback(null, avatarUrl);

Using this will be something like this:
getUserAvatarWithCallback("userIdToFind", function(error, response){
     if(error){console.error("Error", error);}
          console.log("Found the user, url is ", response);

Now can you imagine how the indentation is going inward and inward since in order to do the stuff in a sequential manner we have to keep on making the calls inside the callbacks again and again, that makes the stuff pretty ugly. This is termed as the CALLBACK HELL or PYRAMID OF DOOM.

3. What is a Promise?

A Promise represents a proxy for a value not necessarily known when the promise is created. via Mozilla, here

Now if you go through the definition you find out it says that it is a proxy whose value is not known or available at the time of creation of the promise. So when we make promise we just code the way we do it in other languages.

Let us take an example of Promise using the above example only:
var getUserGithubIdFromDb = function(userId){
     return (new Promise(function(resolve, reject){
          db.getUsers(userId, function(error, response){
var getAvatarUrlFromGithub = function(githubUserId){
     return(new Promise(function (resolve, reject) {        
          github.search.users({q: githubUserId}, function(error, response){

The code above is going to be used as follows:
          console.log("error", error);

If you see this code is pretty maintainable and also is continuous in nature meaning it will be chained to more promises the way we did for 2 functions.

The main thing to note is that at equation (A) we called the reject(error), where reject is the parameter in the Promise constructor which will stop the further execution of the function and throw the error there itself which is going to be caught at (C), and if you are successful in your execution then you have to call resolve(response) [please see equation(B)], where response is passed as a parameter to equation (D), where we have passed it as a parameter to my further processing. This pattern is continuous in nature and you can chain as much promises as you want.