Cynnovative Coding Exercise

Fork this repository, answer the questions in whichever form you want (e.g. .txt, add new README.md files, etc.), build your Dockerized programs in the language of your choice, then submit a pull request with your code.

Question 1 - How big is this file?

The following screenshot is of a file opened in a text editor, with MIME type text/plain, and is seemingly small. What is the file's size in bytes?

I believe the answer is 5 bytes. 1 bytes for each character '0', '.', and '1' and 1 byte each for the carriage return '/r' and the new line '/n' characters. I also double checked this by creating a text file and making its contents match the image and verified that according the OS the file size was 5 bytes.

Question 2 - Python and Switch Statements

The programming language Python does not have a switch construct. What is a way of recreating a switch statement in Python? Write an example that will use the following list of values as cases and actions:

Value: 'red', Action: paintItRed()
Value: 'green', Action: paintItGreen()
Value: 'blue', Action: paintItBlue()
Value: 'default', Action: paintIt()

The python file that implements the switching logic can be found in python-switch directory. I made use of functions and a switcher in order to achieve the switching logic.

Question 3 - StackOverflow and Java

The most copied Java code snippet in StackOverflow has a bug in it:

private static String[] prefix = new String[] {"","K","M","G","T","P","E"};

public static String humanByteCount(long bytes, boolean si) {
    if (bytes == 0) return "0 B";
    int unit = si ? 1000 : 1024;
    double power = Math.min(Math.floor(Math.log(bytes)/Math.log(unit)), 6);
    String pref = prefix[(int) power] + (si && power > 0 ? "iB" : "B");
    String format = power == 0 ? "%.0f %s" : "%.1f %s";
    return String.format(format, bytes / Math.pow(unit, power), pref);
}

Can you find the bug?

I put code in java-bug/JavaBug.java that has the bug fix, but I believe the bug is in the assignment of unit. When si is true, unit should 1024 instead of 1000.

Question 4 - Binary File Analysis

Binary file analysis takes various forms. Write a Dockerized program, in the language of your choice, that finds all the printable strings in an input binary file and prints them out to stdout.

Example of desired functionality:

$ docker build -t $YOUR_DOCKER_IMAGE Dockerfile
$ docker run -it $YOUR_DOCKER_IMAGE find_strings /bin/ls
$ Corresponding Output:
  $FreeBSD: src/bin/ls/cmp.c,v 1.12 2002/06/30 05:13:54 obrien Exp $
  @(#) Copyright (c) 1989, 1993, 1994
  The Regents of the University of California.  All rights reserved.
  $FreeBSD: src/bin/ls/ls.c,v 1.66 2002/09/21 01:28:36 wollman Exp $
  $FreeBSD: src/bin/ls/print.c,v 1.57 2002/08/29 14:29:09 keramida Exp $
  $FreeBSD: src/bin/ls/util.c,v 1.38 2005/06/03 11:05:58 dd Exp $
  \\""
  @(#)PROGRAM:ls  PROJECT:file_cmds-287.40.2
  fffff
  COLUMNS
  1@ABCFGHLOPRSTUWabcdefghiklmnopqrstuvwx%
  bin/ls
  Unix2003
  CLICOLOR
  ...

For this problem, I used the linux function strings which is defined in binutils. The Dockerfile can be found in binary-strings and I built my image using the following command:

docker build -t binary-strings-image -f Dockerfile .

when executed from within the App directory. To run the container, I used the following command

docker run -it binary-strings-image strings /bin/ls

which should output all printable strings.

Question 5 - Circular Prime Numbers

A very interesting mathematical concept is that of circular prime numbers. A circular prime number is a prime number p that, when rearraging its digits, all the possible combinations are also prime.

For example, the number 13 is a circular prime because 13 and 31 are primes.

Create a Dockerized program, in the language of your choice, that finds all the circular prime numbers below 500000.

Example of desired functionality:

$ docker build -t $YOUR_DOCKER_IMAGE Dockerfile
$ docker run -it $YOUR_DOCKER_IMAGE circular_primes
$ Corresponding Output:
  2, 3, 5, 7, 11, 13, 17, 31, 37, 71, 73, ...

The application written in C# using .NET Core 3.1 can be found in the circular-primes directory. The Dockerfile is in circular-primes/App and should be able to be built using:

docker build -t circular-prime-image -f Dockerfile .

when executed from within the App directory. To run the container, I used the following command

docker run -it circular-prime-image

which should output all of the circular primes between 1 and 50000.