This post is a little bit different from the last ones. Days 1-12 followed more or less strictly what HackerRank 30 days of code Tutorial had, but starting on day 13 there was a series of challenges that didn’t allow me to use Go. They are more specific to object-oriented languages like C++ and Java. As Go doesn’t have all the constructions these languages allow, like abstract classes, at least not without a workaround, I decided to take other challenges on HackerRank. The one for today is about statistics and I will introduce some of the concepts before showing the code solution. ...

Inheritance is a nice concept that object-oriented languages have. It is basically the ability for one type, many times called a class or even a struct depending on the language, to inherit the behaviour of another type. HackerRank doesn’t allow me, at least at the moment this post is being written, to submit code in Go for this challenge of inheritance. It seems like Go doesn’t support inheritance, though there are some workarounds that let us mimic the behaviour. The code below is what I tested to mimic the behaviour of a Student class that inherits from the Person class. The Student class has a different printPerson method that calls its super method (the method of the parents class) and it also inherits the sayHello function which is just called by the Student instance object. ...

Hi there! The challenge of today confused me a little in their definition, but they had a good example so it was not hard to get it. Basically I had to read a 6×66 \times 6 matrix and iterate over it summing a pattern of elements like abc d efg that is called an hourglass. So, I just had to iterate through an array and sum 7 elements of it for each iteration. My solution is below. ...

Archiving and compressing are two different concepts. Archiving is basically collecting files in a single package and a popular tool for that is called tar. Compressing is actually reducing file size by means of an algorithm and popular ones include bzip2 and gzip. I will talk about those, but first I would like to talk about another tool for creating archives: cpio. cpio The cpio command can be used to create a backup of the /home/ directory for instance: ...

This post is a collection of commands basically, I hope it works a reference for me and other people who pass by. To delete users, we have deluser and userdel. For me, it was really weird learning that we have two commands with similar names that basically do the same thing. I present some examples below. # removes user and home directory $ deluser -r user $ userdel user # remover user from group $ deluser user group # deleting a group $ deluser --group group Creating or deleting groups, adding a user to them or changing primary group: ...

When a system administrator wants see when a user last changed a password or wants to force a user to change it, there is a really nice command to come to the rescue: chage. I created a user called aluno and I started to check for its information: $ sudo chage -l aluno Last password change : Sep 16, 2016 Password expires : never Password inactive : never Account expires : never Minimum number of days between password change : 0 Maximum number of days between password change : 99999 Number of days of warning before password expires : 7 As we see, the user password was last changed on Sep 16, 2016 and it never expires nor gets inactive. This can be easily changed by using the command chage -M number_of_days and then checking the user info again: ...

The challenge for today is interesting, but I keep wondering if I could do it more efficiently. Let me know in the comments if you have any suggestion after reading my solution. The problem is counting the maximum number of consecutive binary ones in an integer. It is easier to understand with an example: Consider the number 25 represented in base 10 Its representation in binary is 11001 The max number of consecutive ones we can see is 2 What I did was shifting to the right and checking the least significant bit until every single bit of it was checked. The solution is available below. ...

Hi there! Here I am coding again. For those of you readers who may not know what recursion is, I have a brief explanation: a function is called a recursive function when it calls itself. A very nice example is the factorial, which is also what I am going to code today. For the factorial of NN, f(N)f(N), we can state that f(N)=N×f(N−1)f(N) = N\times f(N-1). What we see is that the function is represented by itself, but with other argument and it can keep this going up to a certain point for which we know the answer like f(1)=f(0)=1f(1)=f(0)=1. Given this introduction, I will code. ...

Hi there! The task of today will be coding a phone book. The program reads an integer NN that represents the number of people in the phone book. After that, it reads the NN entries from standard output and generates the dictionary/map. For newbies: dictionaries are the same as maps. Java usually calls the structure with (key, value) pairs as a map, while Python calls it a dictionary. After having the phone book generated, the program will read an unknown number of names. The fact that we can query as many names as we want means that the program needs to check for an end of file before leaving, which is basically trying to read until the user cancels the program. Well, other options would be typing a special quit command, but that’s not the case for this problem. ...

Hi there! A couple days ago I wrote a post about a simple array sum in Go and I said I didn’t need an array in memory to do the sum, but just an integer that would store the inputs the user gave the program. This time, I will really need an array. The goal is to read an array AA of NN elements and print AA elements in reverse order. Surely I could put everything in a file and then read it backwards, but as I don’t even know how to use files in Go at the moment, I will be creating an array in memory and then printing it backwards to the screen. My solution is just below. ...