SHAN'S SOLUTION

Leetcode 78 : Subsets

noreply@blogger.com (SHAN'S SOLUTION) — Mon, 24 Aug 2026 21:49:06 +0000

Subsets on the Stack

Recursion · Backtracking · The call stack

Subsets on the Stack

Every subset of a set is one path through a tree of yes/no decisions. Watch the machine walk that tree — pushing a frame each time it goes deeper, popping one each time it comes back.

Input set { 1, 2, 3 } → expect 2³ = 8 subsets

The machine

Step through it

The tree shows where you are. The stack shows how you got there — one frame per unfinished call, each one paused mid-line, waiting for the call above it to finish.

start Press Play, or step with the arrow keys.

Code · current line

1void findSubsets(int index) {2    if (index == nums.length) {3        results.add(new ArrayList<>(current));4        return;5    }6    current.add(nums[index]);          // TAKE7    findSubsets(index + 1);            // explore8    current.remove(current.size()-1);  // UN-TAKE9    findSubsets(index + 1);            // SKIP10}

Call stack

current (the shared bag)

empty

results

0 / 8 recorded

step 0 / 0

Keyboard: ← and → step, space plays and pauses.

The thing that confuses everyone

Two kinds of memory, only one of which cleans itself up

Every frame on that stack carries its own copy of index. Java saves and restores it for you — that is what a stack frame is. But there is only one current list in the entire program, shared by every frame. Nobody restores it for you.

index — per frame, automatic

frame 4index = 3

frame 3index = 2

frame 2index = 1

frame 1index = 0

Four live frames, four separate index values, each sealed inside its own frame. When a frame pops, its index vanishes with it and the caller finds its own value exactly as it left it.

You never write code to restore index. The hardware stack does it.

current — one object, shared

↓ ↓ ↓ ↓

current = [ 1, 2, 3 ]

all four frames point here

Every frame holds a reference to the same ArrayList. A frame that adds to it has changed the world for its caller too — the change outlives the frame that made it.

So the caller must undo it by hand. That is the whole job of line 8: current.remove(...) is the manual restore for the one piece of state the stack won't restore for you.

The stack restores what belongs to a frame. You restore what everyone shares.

Reading the picture

Five things the animation is showing you

Going down = pushing. Line 7 and line 9 are the only two places the stack grows. Each one is a question: “what happens if I take it?” and “what happens if I don't?”
The paused frames are the path. The frames below the top aren't idle — each is frozen mid-line, holding the return point. Read the stack bottom-to-top and you read the highlighted path down the tree.
Recording happens only at leaves. A subset is complete only when there are no decisions left. That's index == nums.length — the base case, the only place anything is written to results.
Backtracking happens on the way up. Line 8 runs after a whole branch has finished and returned. That's why it doesn't look like it belongs where it sits in the code.
The tree is never built. There's no tree object in memory — only the current root-to-node path, alive as stack frames. Everything to the left has been popped; everything to the right doesn't exist yet.

The cost

Why the stack stays small even though the answer is huge

The tree has 15 nodes and 8 leaves, but at no moment do more than 4 frames exist. The machine walks the tree depth-first, so it only ever holds one root-to-leaf path — which is why recursion depth is n + 1, not 2ⁿ.

Quantity	For n = 3	In general
Subsets produced	8	2ⁿ
Nodes in the tree	15	2ⁿ⁺¹ − 1
Max frames alive at once	4	n + 1
Time	~24 ops	O(n · 2ⁿ)
Stack space	4 frames	O(n)

Total steps in this trace: —. Every one of them is a push, a pop, an add, a remove, or a record. There is nothing else in backtracking.

Choose. Explore. Un-choose. The stack handles the rest.

Download binaries like pom, jar and dependencies from an artifactory and save it in a local directory | Migrate dependencies from one repository to another | Using maven , pom.xml

noreply@blogger.com (SHAN'S SOLUTION) — Wed, 17 May 2023 17:18:00 +0000

Structure of pom.xml

https://github.com/shankhadeepk/dependencydownloader/blob/main/pom.xml

Then go the location where the project is and run command

mvn clean install

A folder will be created at the location ([project]/target/[location as shown below]) which is given by following properties in the pom.xml

<outputDirectory>${project.build.directory}/lib</outputDirectory>

Enable newly installed java for your favorite browsers

noreply@blogger.com (SHAN'S SOLUTION) — Wed, 10 Feb 2016 15:08:00 +0000

For Mozilla
64 bit Jdk
sudo ln -s /usr/lib/jvm/jdk1.8.0/jre/lib/amd64/libnpjp2.so /usr/lib/mozilla/plugins
32 bit jdk
sudo ln -s /usr/lib/jvm/jdk1.8.0/jre/lib/i386/libnpjp2.so /usr/lib/mozilla/plugins
For Chrome
64 bit jdk
sudo mkdir /opt/google/chrome/plugins
sudo ln -s /usr/lib/jvm/jdk1.8.0/jre/lib/amd64/libnpjp2.so /opt/google/chrome/plugins
32 bit jdk
sudo mkdir /opt/google/chrome/plugins
sudo ln -s /usr/lib/jvm/jdk1.8.0/jre/lib/i386/libnpjp2.so /opt/google/chrome/plugins

Install any oracle java in your Ubuntu 15.10

noreply@blogger.com (SHAN'S SOLUTION) — Wed, 10 Feb 2016 15:01:00 +0000

Step 1: Download the preferable jdk from oracle web site. Here we will use
jdk version as jdk-8-linux-x64
Step 2: Keep the tar.gz file in a folder of your choice in /home/ directory.
Step 3: Extract the tar.gz file
tar -xvzf jdk-8-linux-x64.tar.gz

Step 4: Create JVM folder in /usr/lib folder like:
sudo mkdir /usr/lib/jvm

Step 5: Move the extracted jdk to the above location like :
sudo mv jdk1.8.0 /usr/lib/jvm/jdk1.8.0

Step 6: Install new java sources in system like:
sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk1.8.0/bin/javac 1
sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk1.8.0/bin/java 1
sudo update-alternatives --install /usr/bin/javaws javaws /usr/lib/jvm/jdk1.8.0/bin/javaws

Step 7: Choose default Java
sudo update-alternatives --config javac
sudo update-alternatives --config java
sudo update-alternatives --config javaws

Step 8: Check the java version.
java -version

Change the Heap Size and Stack size in Java's JVM

noreply@blogger.com (SHAN'S SOLUTION) — Wed, 04 Feb 2015 14:19:00 +0000

In order to change the heap size, there are two parameters that need to be updated :

-Xms512m
-Xmx1024m

These parameters can be found in eclipse.ini file in the eclipse folder.

To change the stack size, there is a parameter that need to be updated :

-Xss512m

Code for reversing a string in Java

noreply@blogger.com (SHAN'S SOLUTION) — Sun, 09 Mar 2014 20:14:00 +0000

package com.reverse;

public class ReverseWords {

public static String reverseTheString(String input)
{
if(input.length()>1)
return input.substring(input.length()-1, input.length()) + reverseTheString(input.substring(0,input.length()-1));
else
{
return input.substring(0, 1);
}

}
public static void main(String args[])
{
System.out.println(reverseTheString("hello"));
}

}

Enable java plugin for firefox in Ubuntu

noreply@blogger.com (SHAN'S SOLUTION) — Sat, 14 Jan 2012 14:03:00 +0000

The java run time environment can be downloaded from the java site. Run the command for make the plugin work for Firefox in Ubuntu
$cd /usr/lib/mozilla/plugins
$sudo ln -s /usr/lib/jvm/jre1.6.0_30/plugin/i386/ns7/libjavaplugin_oji.so

Use Tata photon + in Ubuntu 10.04

noreply@blogger.com (SHAN'S SOLUTION) — Mon, 08 Nov 2010 19:59:00 +0000

unplug and plug Tata photon + and execute the command
$ sudo usb_modeswitch -c /etc/usb_modeswitch.d/12d1:1446
The usb_modeswitch needs to be installed in the ubuntu 10.04

Play AVI,MP3 and all media file in UBUNTU

noreply@blogger.com (SHAN'S SOLUTION) — Sat, 23 Oct 2010 18:58:00 +0000

$ sudo wget --output-document=/etc/apt/sources.list.d/medibuntu.list http://www.medibuntu.org/sources.list.d/$(lsb_release -cs).list

$ sudo apt-get --quiet update

$ sudo apt-get --yes --quiet --allow-unauthenticated install medibuntu-keyring

$ sudo apt-get --quiet update

$ sudo apt-get install non-free-codecs

$ sudo apt-get install libdvdcss2

$ sudo apt-get install w32codecs

$ sudo apt-get install vlc mplayer

Download Mplayer

noreply@blogger.com (SHAN'S SOLUTION) — Wed, 15 Apr 2009 06:41:00 +0000
http://rpmfind.net/linux/rpm2html/search.php?query=mplayer-skins&submit=Search+...&system=&arch=
http://rpmfusion.org/Configuration/
http://www.mjmwired.net/resources/mplayer-fedora.html#config2

Change Repository from Livna to Freshrpms in FEDORA 8

noreply@blogger.com (SHAN'S SOLUTION) — Tue, 18 Nov 2008 01:07:00 +0000
Follow some simple steps:
# sudo rpm -hiv http://ftp.freshrpms.net/pub/freshrpms/fedora/linux/8/freshrpms-release/freshrpms-release-1.1-1.fc.noarch.rpm
#sudo rpm --import http://freshrpms.net/RPM-GPG-KEY-freshrpms

Install Flash Player for firefox 64 bit in FEDORA 8

noreply@blogger.com (SHAN'S SOLUTION) — Sat, 15 Nov 2008 08:13:00 +0000
Just follow some important steps as follows:
# rpm -ivh http://linuxdownload.adobe.com/adobe-release/ adobe-release-i386-1.0-1.noarch.rpm # rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-adobe-linux # mkdir -p /usr/lib/mozilla/plugins # yum install nspluginwrapper.{i386,x86_64} pulseaudio-lib.i386 # yum install flash-plugin # mozilla-plugin-config -i -g -v

Having problem while using intel 945GCNL motherboard? Damn the Fedora core 6 cannot detect the ethernet card! ......Well here is the solution

noreply@blogger.com (SHAN'S SOLUTION) — Sun, 06 Jan 2008 19:53:00 +0000
If you have Windows XP or Windows 98 in your PC with Fedora Core ,then go to Win and see the hardware manager .Search for the name of the ethernet card.Find a suitable driver from the net.Install the driver in Fedora Core 6.So,your ethernet card is ready.....njoy the net. In case of INTEL 945GCNL Its Realtek RTL8168/8111 To download the driver click here.

CONFIGURATION OF BSNL DATAONE BROADBAND SERVICE [using Huawei SmartAX MT880 ADSL router]

noreply@blogger.com (SHAN'S SOLUTION) — Mon, 03 Sep 2007 08:14:00 +0000
The router configuration is specific to Huawei SmartAX MT880 ADSL router. System Configuration

Login as root.
Select System Settings > Network or system-config-network-gui on terminal.

You'll see your NIC listed there. Select it and click Edit.
Check Activate device when computer starts and Allow all users to enable and disable this device.
Select "Statically set IP addresses"

Enter the following values
Code:

Address : 192.168.1.2
Subnet Mask : 255.255.255.0
Default gateway address : 192.168.1.1

Press OK.
Press Activate.

open /etc/resolv.conf in your favourite text editor
Append the following lines.

Code:
nameserver 61.1.96.69
nameserver 61.1.96.71

Router Configuration

Now start your Web Browser and type 192.168.1.1 in the address bar and press enter.

PS: Enable JavaScript in your browser, if not.

It will ask for username and password. Use admin as username and password.

Click on WAN Settings under Home in the left pane.
If not set, enter the following values

Code:
PVC No: PVC-0
Wan Type: PPP
Connection Type: PPPoE VPI/VCI: 0 / 35
Default Route : Enabled PPP
Username: yourusername
Password: yourpassword
Use DNS: Enabled
Max Idle Time: Always On

Click Apply
When asking for save and reboot, select No and Press OK.

Now click on DNS under Home on left pane.
If not set, enter the following values
Code:

DNS Status: Enabled
Primary DNS Address: 61.1.96.69
Secondary DNS Address: 61.1.96.71

Click Apply
When asking for save and reboot, select No and Press OK.

Now click on LAN Settings Under Advanced on left pane.
If not set, enter the following values
Code:

IP Address: 192.168.1.1
Subnet Mask: 255.255.255.0

Click Apply
When asking for save and reboot, select Yes and Press OK.

The device will reboot now. It will take about two minute or more.

Do not refresh or close the browser window while rebooting. It's better leave your computer alone while this operation.

After the device has been rebooted, refresh the page. Now scroll down and you should see the green light for LAN and WAN (PVC-0)Channels.

Now click on Diagnostics under Status on left pane.

On Clicking Submit, it will do a series of tests.

Important thing is that the result of first 3 under Modem Connection Test must be PASS. Don't care others.

Now, you're done. Your machine will be connected to the internet from next reboot onwards and will be always on. If you still prefer manual connect/disconnect, uncheck the Activate device when computer starts option from network configuration window. you can use the following commands

for connecting - ifup eth0
for disconnecting - ifdown eth0

provided the device name of your NIC is eth0.
You can create launchers on Desktop/Panel for the same.

Reboot your machine and Enjoy DATAONE SERVICE!!!

The simplest way of checking BSNL DATAONE usage in Fedora Core

noreply@blogger.com (SHAN'S SOLUTION) — Tue, 07 Aug 2007 22:53:00 +0000

I used IE 6 in Linux for checking my Dataone usage through Fedora Core 6.But,it would have been much better if I could check my usage through my Firefox Browser.I tried everything in Firefox and guess wat I finally solved it.Just click the link given below from ur FireFox browser and check ur monthly usage just u do in ur IE6 browser.

BSNL Broadband usage

Another Way To Check BSNL Dataone Usage

noreply@blogger.com (SHAN'S SOLUTION) — Sun, 15 Jul 2007 19:45:00 +0000

--> This has been helpful for me and hope will also help you.As I am using Fedora Core6 ,it has been difficult for me to check my account.Then I used the DataFox.But,the safest is IE for Linux.
I know you people are not intrested in using IE in Linux but it really works in checking the Dataone Account safely.

It's actually quite easy ,thanks to some very handy scripts from IEs4Linux. Before you start you'll need to make sure you have wine and cabextract installed:

# yum -y install wine cabextract
$ gtar xzvf ies4linux-2.0.5.tar.gz
$ cd ies4linux-2.0.5
$ ./ies4linux
Welcome, greg! I'm IEs4Linux.
I can install IE 6, 5.5 and 5.0 for you easily and quickly.
You are just four 'enter's away from your IEs.
I'll ask you some questions now. Just answer y or n (default answer is the bold one)
IE 6 will be installed automatically.
Do you want to install IE 5.5 SP2 too? [ y / n ] y
.
.
.
IEs 4 Linux installations finished!
To run your IEs, type:
ie6
ie55
ie5
Start the IE and open the famous portal for checking the BSNL Broadband usage and do as you used to do while using Windows.
do as you used to do while using Windows.

Then just download the latest script, extract and run it. The example below is based on version 2.0.5, just adjust the version number as necessary. Please note that you will want to install and run this as your own user, NOT as root. I used the defaults except that I installed all the versions of IE. I do some web development and I always find myself needing to resolve some goofy incompatibilites with older versions of IE.

DataFox to check the usage of Dataone Broad Band Service In LINUX

noreply@blogger.com (SHAN'S SOLUTION) — Fri, 13 Jul 2007 09:17:00 +0000
DataFox is an easy to use, cross platform & customizable extension to Firefox, which you can use monitor your DataOne Broadband bandwidth usage. It is not a standalone program and will only work when installed as an extension to Firefox. DataFox is non-intrusive and does not monitor your network activity, it just obtains the information from the BSNL website. The collected info is displayed in your Firefox status bar area and additional info is displayed in a tooltip.

Here are a couple of screenshots:
I have been really irritated by the fact that I could not easily check my usage in Firefox, and I really would like to do so frequently, so I didn't want to use a separate program. Since Firefox is always open on my machine, writing a Firefox extension to do this seemed logical. DataFox does not collect statistics, past records or draw graphics - not yet anyway. The goal here is simplicity, all that matters to me is how much bandwidth I've used and how much I have left until the month ends. I've also added the ability to allow Firefox to browse the usage site directly, so if you need the details, you can get them - without switching to IE. DataFox obtains the info it displays from the summary provided in the BSNL site for a given month, it does not read all your records and make it's own totals.

More info and the download is available here: Download DataFox

Rajabazar Science College as seen from Space

noreply@blogger.com (SHAN'S SOLUTION) — Wed, 11 Jul 2007 14:53:00 +0000
This is how the institution looks from Space.Its an image by the satellite.

University College Of Science And Technology,Rashbehari Siksha Prangan (Rajabazar Science College)

noreply@blogger.com (SHAN'S SOLUTION) — Wed, 11 Jul 2007 14:38:00 +0000
University College of Science and Technology is the Science and Technology college under University Of Calcutta.The college is also well renowned by the name Rajabazar Science College.Science and Technological Post Graduate courses are being conducted by the institution.The author is persuing his Post graduate course from this college.The institution has a history of excellence.University Of Calcutta is the oldest university in Asia with a history of about 150 yrs.Renowned companies are recruiting the students of the University.

If anyone wants to add something to this they are most welcomed.Their comments will be incorporated.

Optimize Memory

noreply@blogger.com (SHAN'S SOLUTION) — Fri, 20 Apr 2007 04:48:00 +0000
Inorder to optimize your memory Just create a shortcut on the desktop and add the path as follows %windir%\system32\rundll32.exe advapi32.dll,ProcessIdleTasks

Objective

noreply@blogger.com (SHAN'S SOLUTION) — Sun, 27 Aug 2006 16:23:00 +0000
The main objective of the blog is to help the users solve simple problems faced while using different Operating Systems .