30 days of code in Go: Day 14 - Weighted mean

Hi there! Today’s problem is quite simple. The challenge is to compute the weighted mean given two arrays. The first input is $N$, the number of elements of each array, and then the first array is given and then the second whose components are the weights. My solution is given below. package main import "fmt" func main() { N := 0 fmt.Scanf("%d", &N) a := make([]float64, N) b := make([]float64, N) for i := 0; i < N; i++ { fmt....

September 30, 2016 · 1 min

30 days of code in Go: Day 13 - Mean, Median and Mode

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....

September 29, 2016 · 3 min

30 days of code in Go: Day 12 - Inheritance (kind of)

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....

September 18, 2016 · 3 min

30 days of code in Go: Day 11 - 2D Arrays

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 $6 \times 6$ 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....

September 17, 2016 · 2 min

Archiving and compressing files in Linux

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:...

September 17, 2016 · 3 min

More admin commands for users in Linux

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:...

September 17, 2016 · 2 min

Administrating Linux users with the chage Command

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....

September 16, 2016 · 3 min

30 days of code in Go: Day 10 - Binary Numbers

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....

September 16, 2016 · 1 min

30 days of code in Go: Day 9 - Recursion

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 $N$, $f(N)$, we can state that $f(N) = N\times f(N-1)$. 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 $f(1)=f(0)=1$....

September 15, 2016 · 1 min

30 days of code in Go: Day 8 - Dictionaries and Maps

Hi there! The task of today will be coding a phone book. The program reads an integer $N$ that represents the number of people in the phone book. After that, it reads the $N$ 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....

September 14, 2016 · 3 min