Monday, 31 July 2017

Install Oracle instant client and sqlplus using Homebrew


 In one of the previous posts we say how to install and run sql plus  and Oracle instant client  on Ubuntu operating system -
In this post we will see the same for a Mac.

This post expects you have homebrew installed. If not please refer -

 Install Oracle instant client and sqlplus using Homebrew

For this you need to download following two files -
You can download these files from oracle site -

Once download copy these files into following folder-
  •  ~/Library/Caches/Homebrew 
 Once done run following commands -
  • brew tap InstantClientTap/instantclient
  • brew install instantclient-basic
  • brew install instantclient-sqlplus
 This should install sqlplus for you.

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Friday, 28 July 2017

How to Disable a MacBook’s Built-In TrackPad When Using a Mouse or Wireless Trackpad


For me this became a requirement as my trackpad started malfunctioning. But it can be a useful feature as well. When we connect a mouse we would not want trackpad to work. For eg. lets say you are playing counter strike with a mouse you definitely don't want trackpad to change your aim in game. So it would be better if you disable in build trackpad while mouse is connected. In this post I will show you how you can do this.

Disable Trackpad in OS X Lion and Above

For this you need to go to -
  • System Preferences > Accessibility > Mouse & Trackpad
Here you will find a checkbox saying "Ignore built-in trackpad when mouse or wireless trackpad is present". Click it and make sure you have checked it. Setting should take effect immediately.

Disable Trackpad in OS X Snow Leopard

Setting is the same here too. It's just at different path. So head to 
  • System Preferences > Universal Access > Mouse & Trackpad
Here again you will find the same checkbox. Check it and you should be good to go.

Sunday, 9 July 2017

How to install wine and run windows programs on your mac


Sometimes it becomes necessary to install windows program on your Linux or mac machine. Like I mentioned in a post sometime back there may be some sites that require IE only -
In this post I will show you how to install wine on your mac. Wine is a very handy software that allows you to install and run windows programs in a windows like simulated environment.

Installing Wine on Mac

You need to have homebrew installed on your mac. If not please refer -
 Next Homebrew uses an extension called Homebrew Cask to install other programs. You can install the Cask extension by running following command -
  • brew tap caskroom/cask

Wine needs -
  • Java and 
  • XQuartz 
as dependencies to be already installed. I am assuming you already have Java installed on your machine and set it up in classpath. You can install  XQuartz with following command -
  • brew cask install xquartz

NOTE :  You can similarly install Java if you already done have it -
  • brew cask install java
 Once dependencies are done you can directly install wine with following command -
  • brew install wine

Also install winetricks -
  • brew install winetricks

 Use winetricks to set environment as windows 7 -
  • winetricks win7

Installing and running Windows program from wine

Go to the directory where you have downloaded your exec file and run -
  • wine installer.exe
where installer.exec is your exe file.

 You can find installed files in dir -
  • /Users/athakur/.wine/drive_c
You can then navigate to program files, find your installed program and run it -

 Once in the program directory you can simply run it as -
  • wine ioexplorer.exe

And you are done :)

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How to check if a Singly Linked List is a Palindrome or not


This is another classic data structure interview question that fall into basic DS problems. You might have seen or known method to find if a String is palindrome or not. You can simply iterate on half of the String and check with reversed other half if it same.

Time Complexity : O(N)
Space Complexity : O(1)

It will be as simple as -

    public static boolean isPalindrome(String str) {
        if(str == null) {
            return false;
        for(int i = 0; i< str.length()/2; i++) {
            if(!(str.charAt(i) == str.charAt(str.length() - i - 1))) {
                return false;
        return true;

Test :

It can have a variant such that instead of a String you have a Linked List. Now if you have a double linked list it becomes very easy. You start from head and from the tails and keep comparing. Increment the header pointer and decrement the tail pointer in each iteration. Time complexity will be O(N) only.

However the question at hand is of Singly Linked List.

How to check if a Singly Linked List is a Palindrome or not


Method 1 : Using a String


Iterate over the Linked list and construct a String out of it and then check if that String is a Palindrome.Time complexity O(N) but space complexity is also O(N) since you are now creating a String.

Since interviewer asked you Linked List this is most definitely something he does not want. He could have asked a String palindrome itself if that was the case. But it never hurts to put it out what you are thinking and build upon your answer as you proceed.


Method 2 : Using a Stack


You can iterate over the Linked List put it's content in stack. Once iteration is over we can iterate over Linked List again and this time with each iteration compare Nodes content with Stacks popped out content. If it does not match it is not a palindrome.
This again has time complexity O(N) and space complexity O(N).

1) Traverse the given list from head to tail and push every visited node to stack.
2) Traverse the list again. For every visited node, pop a node from stack and compare data of popped node with currently visited node.
3) If all nodes matched, then return true, else false.

Code :

    public static boolean isPalindrome(ListNode<String> head) {
        boolean isPanindrome = true;

        Stack<String> stack = new Stack<>();
        ListNode<String> currentNode = head;

        while (currentNode != null) {
            currentNode = currentNode.getNext();

        currentNode = head;
        while (currentNode != null) {
            if (!currentNode.getValue().equals(stack.pop())) {
                isPanindrome = false;
            currentNode = currentNode.getNext();
        return isPanindrome;

I have also added it to my Data Structure github repo. Check isPalindrome() method in 


Method 3 : Reversing the 2nd half of the Linked List


This is a better version and always one you should aim for. It provides O(N) time complexity and O(1) space complexity -

1) Get the middle of the linked list.
2) Reverse the second half of the linked list.
3) Check if the first half and second half are identical.
4) Construct the original linked list by reversing the second half again and attaching it back to the first half

4th point is optional and depends if you need original List back.

I have added it to my Data Structure github repo. Check isPalindrome2() method in  


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How to display or hide line numbers in vi or vim text editor


Line number come in very handy when you are working with any Text Editor. However if you take vi or vim editor then line numbers are hidden by default. In this post we will see how we can turn it on.

How to display or hide line numbers in vi or vim text editor

This post assumes you are a vim user and are aware of basic usage. Like for example when you need to save and quit data in vim you-
  • press escape followed by :wq
or if you want to exit without saving
  • :q!
 vi support a lot of commands to use and  options to be set by using colon (:)

To show line numbers in vi simple type below are pressing escape -
  • :set number OR
  • :set nu
 To hide it you can type -
  • :set nu! OR
  • set nonumber

This you need to do every time you launch into vi editor. To make it default edit your file at location ~/.vimrc and append following line at the end -

  • set number
NOTE : You can create this file if it does not exist already.

Now you will always get line numbers when you launch vim editor.

 Now that we have seen how to hide and display line numbers in vim editor lets see how we can jump to a particular line in vim -

How to jump to a particular line in vim

This is also fairly simple. Once you have launched vim you can simply move to any line number using following command -
  • : linenumber
  • :6

 You can ever jump directly to your line number immediately as you open vim. To do that use following command while opening vim -
  • vi +linenumber filename
  •  vi +6 test.txt
This should open your file and move to the linenumber you have provided.

General Info

vim provides a lot of configurable options to set. To see them all type following command -
  • :set all

To see everything that you have set so far you can type following command -
  • :set
For me it is as follows -

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