Finding overall and per core CPU utilization

Today I will post about how to monitor CPU usage by processor in Linux. As you might have expected this will simply access the CPU time information from /proc pseudo-filesystem and report the results.

The proc filesystem or the Procfs is a special filesystem which gives you a view into the kernel data. No files in procfs exists actually in the disk. There is no disk inodes and thus storage related to the files. Instead of going into procfs I will redirect you to wikipedia: http://en.wikipedia.org/wiki/Procfs. Let’s get in.
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C Q&A #6: An interesting difference between the C and C++ conditional operator

int main (void)
{
  int a = 5, b = 10, c;

  c = a > 3 ? b = 5 : a = 3;
  printf ("%d %d %d\n", a, b, c);
  //cout << a << " " << b << " " << c << endl;
  
  return 0;
}

Have a look at the above code, what will be the outcome if the code was in C language and if in C++ Language (replace with printf with cout)?

Directly going to the solution. Compilation error for C, and works perfect (no warnings) with C++. I saw this problem is a C question and answer book which didn’t bother to explain, so here is the explanation. Continue reading “C Q&A #6: An interesting difference between the C and C++ conditional operator”

Find pairs of numbers in an array with difference ‘k’

The problem statement is, an long array is given with n elements, we need to find all the pairs of numbers in this long array which have a constant difference k. I will post three methods. The first method is the brute force method and has a runtime complexity O (n2), the next method has runtime complexity O (n*log (n)), and the last one will have the runtime complexity O (n).

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Jumble word solver again

I have already posted a jumbled word solver written in C language, although what I posted is actually become old, as I have changed some of the things in the code. I will update the post with this (hope to update!) with the new changes, but before it I would like to post the the same stuff in other languages and with different datastructure. Recently I am learning Perl and brushing up C++, therefore I will post jumble word solver written in C++ and Perl in this post.
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Implement queue using stack

The puzzle is to implement basic queue operations with using only basic stack operations. That is, a stack object is given, we need construct a wrapper for the queue functions, insert, remove, which will only use the stack object as its storage, and naturally will have to use the stack operations. I have already posted the opposite task in the post Implement stack using a queue

This can be done using two stack objects. We call these the first stack and the second stack. Although either the insert or the remove complexity will no more be O(1).

I have discussed the process gradually. I added the last solution when it clicked in my mind while reviewing this post.

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Plot histogram in terminal

We had assignments to print “*”s in different formation in undergraduate class, which I never liked as they were pointless. Now I got a somewhat justifiable application, plot histogram in terminal. In the last post Generating random numbers from Normal distribution in C I posted the C code to generate random numbers from the Normal distribution using the Polar method. In this post I am posting a simple code to plot the histogram of generated random numbers from this or any other distribution. Let me first post the code and then explain what is going on. Continue reading “Plot histogram in terminal”

Generating random numbers from Normal distribution in C

I needed to write a random number generator in C which will generate random numbers from Normal Distribution (Gaussian Distribution). Without this component I couldn’t proceed to finish writing a C code for Heuristic Kalman Algorithm by Lyonnet and Toscano for some experiments. I selected the Marsaglia and Bray method also known as the Polar method to generate Normal random variables. Here is how it is done. Continue reading “Generating random numbers from Normal distribution in C”