Problem with Hp laptop and Ubuntu

I installed Ubuntu on my HP pavillion ab series (i7 processor).
Ubuntu was running just fine when I realized it is not able to detect to my home wifi but able to connect to my phone hotspot.
I had faced similar problem in opensuse earlier but then I removed it considering no driver support for my wifi module (Network controller: Realtek Semiconductor Co., Ltd. RTL8723BE PCIe Wireless Network Adapter
).
I started googling stuff and finding peers which were facing similar problems. After sleeping over the problem, I had one crazy observation. The difference between my phone's hotspot and wifi router was the distance from my laptop. I took my laptop and stood next to the wifi router, and found out that it was able to detect wifi over there. Voila.

Then I googled in this direction and found out that it is a problem.
  

sudo tee /etc/modprobe.d/rtl8723be.conf <<< "options rtl8723be ant_sel=1"

Fired this command ,then restarted my laptop.

It worked.

Thanks to
https://askubuntu.com/questions/872931/how-to-make-wifi-signal-stronger-on-ubuntu-16-04-lts
https://connectwww.com/how-to-solve-realtek-rtl8723be-weak-wifi-signal-problem-in-ubuntu/4625/

Cheers !!

Hackerrank 'Army game problem'

This post is dedicated to Hackerrank 'Army game problem'.

Here is the question:

Luke is daydreaming in Math class. He has a sheet of graph paper with  rows and  columns, and he imagines that there is an army base in each cell for a total of  bases. He wants to drop supplies at strategic points on the sheet, marking each drop point with a red dot. If a base contains at least one package inside or on top of its border fence, then it's considered to be supplied. For example:

Given  and , what's the minimum number of packages that Luke must drop to supply all of his bases?

Input Format

Two space-separated integers describing the respective values of  and .

Constraints

Output Format

Print a single integer denoting the minimum number of supply packages Luke must drop.

Sample Input 0

2 2

Sample Output 0

1

Explanation 0

Luke has four bases in a  grid. If he drops a single package where the walls of all four bases intersect, then those four cells can access the package:

Because he managed to supply all four bases with a single supply drop, we print  as our answer.

Answer:

There are multiple approaches to solve this but I would like you guys to try it for some time then look below. 

I know you guys did not try , just googled it :D.

You can consider this as denomination problem where you need to split the matrix in amounts of 2X2 , 1X2 and 1X1. This is a broad solution and a bit tricky as well ,since you need to keep a count each and every row. 

For the next bit think a bit out of the box. I mean literally out of the box .

Now try and cover this whole by just 2X2 even if you go out of the box.

Give it some time use a paper and pen you will find the pattern hidden there only.

Let me break it down for you.

Consider a  10X6 matrix 

Now for a 10X5 matrix :

Total Number of supply drops are same in both cases.

Since 10X5 and 10X6 could be fit in 10X6 matrix.

Now test for odd row and column. It has a bit of tweak in it.

I have pasted the code in C++ for your reference. I know you will copy it . So go ahead.

I am not saying it is most optimized code since there is always a room for optimization. Wrote it as I thought about it. Hope you find it useful. 

CODE:

int main(){   
     int n;    
     int m;
    cin >> n >> m;
    int twobytwo  = (m / 2) * (n / 2);
    int factor =0;
    if( (m%2 ==1) && (n%2 ==1) ){ 
       factor = ( (m/2 +1) + ((n-1) /2) );
     }else if(m%2 == 1){
        factor = n/2;
    }else if(n%2 == 1){
        factor = m/2;
    } 
   cout <<(twobytwo+factor);
    return 0;
}

Linux Kernel Development 1.0

Some things before you start:-

• check you kernel version => uname -r
• you will get an version name and local version. e.g.... (3.2.0-4-amd64)

• then search for your source tree ... it should be in /usr/src/ ... if not found there
• download you Linux source tree with exact version . in my case it will be Linux 3.2.0. Google it and you will get a zip file. Extract it under the folder /usr/src/

• now you need to run some commands
• first go into the kernel source directory then follow these steps 
• make menuconfig (if you want to customise your kernel)
• make -j<number of cpus>
• make install 
• make modules_install
• Now your kernel is ready

For more digging on above section go to "http://unix.stackexchange.com/questions/20864/what-happens-in-each-step-of-the-linux-kernel-building-process" . This will help you.

Here it starts:-

• You need two things first is your driver code(c file) and next is Makefile.
• This is a hello world program for kernel. Save it in hello.c
  #include <linux/module.h>
  #include <linux/kernel.h>
  
  int init_module(void)       //this function runs when your module is loaded
  {
     printk("Hello world");
     return 0;
  }
  void cleanup_module(void)   //this function runs when your module is unloaded
  {
    printk("Goodbye world \n");
  } 
  MODULE_LICENSE("GPL");  //compulsory part in every driver code

• Now in Makefile .... be sure to name the file as Makefile (capital M don't forget):-
  obj-m := hello.o           //same as your module name with an .o extension

• Something you must not do:-
• compile the program to get (.o)  . Makefile will take care of that.
• Now write this command on the terminal.
  make -C /usr/src/"your Linux version" M=`pwd` modules

• If every thing goes write then you will see 6 files generated . You can inspect all of them and dig them vigorously . The file which is of your use is the one with .ko extension. it is a dynamic loadable module. go and read about it !! 
• Since you have a dynamic module its time you load it !! Here is the command 
• insmod <dynamic module>
• you might require root privileges so use sudo 
• open dmesg and check whether all you wrote in the printk is there or not. you can use grep to find it . dmesg is the kernel ring buffer which gives us the details provided by the kernel messages.
• Since you have loaded it now its time to remove it.
• rmmod <dynamic module>
• This is it !! you have created a kernel module. 
• Amount of efforts put in to write a hello world  for kernel is high but if you love hardware then this is how it is going to be !!