Monthly Archives: January 2018

The “Eiffel” (I fell) Tower and the “I did not fall” Tower

Eiffel tower image source:


I do not know what is worse, having high blood pressure or the fact that my mum and my wife know about it

ffmpeg: Create a video countdown

The code below was used to generate the video countdown timers that are available in the following playlist using ffmpeg:

#This example will create a 3 second video, with 100 frames per second and it will print the elapsed and remaining times using a two second accuracy.
ffmpeg -loop 1 -i ~/Pictures/Black-Background.png -c:v libx264 -r $fps -t $seconds -pix_fmt yuv420p -vf "fps=$fps,drawtext=fontfile='/usr/share/fonts/urw-base35/C059-Bold.otf':fontcolor=yellow:fontsize=$upperFont:x=(w-text_w)/2:y=(h-text_h)/2:text='%{eif\:($seconds-t)\:d}.%{eif\:(mod($seconds-t, 1)*pow(10,$mantissaDigits))\:d\:$mantissaDigits}',drawtext=fontfile='/usr/share/fonts/urw-base35/C059-Bold.otf':fontcolor=yellow:fontsize=$lowerFont:x=(w-text_w)/2:y=((h-text_h)/2)+$upperFont:text='Elapsed\: %{eif\:(t)\:d}.%{eif\:(mod(t, 1)*pow(10,$mantissaDigits))\:d\:$mantissaDigits}'" "$seconds seconds countdown timer.mp4";


  • We used a single black frame for the background that defined the size of the video frame as well.
  • Using the fps variable we defined the number of Frames per Second for the video.
  • The seconds variable defined the number of seconds the duration of the video should be.
  • The mantissaDigits variable defines how many decimal digits should be shown after the dot.
  • upperFont and lowerFont define the size of the fonts in the upper row and the lower one respectively.
  • We used the drawtext directive twice to write to the frames.

Notes on the first drawtext:

  • fontfile='/usr/share/fonts/urw-base35/C059-Bold.otf' defines the font to be used for the text.
  • fontcolor=yellow defines the color of the font of the text.
  • fontsize=$upperFont defines the size of the font of the text.
  • x=(w-text_w)/2 defines the X-coordinate of the location for the text on the frame, here we center the text horizontally on the frame.
  • y=(h-text_h)/2 defines the Y-coordinate of the location for the text on the frame, here we center the text vertically on the frame.
  • text='%{eif\:($seconds-t)\:d}.%{eif\:(mod($seconds-t, 1)*pow(10,$mantissaDigits))\:d\:$mantissaDigits}' We print the remaining seconds for the video to finish with specific decimal digit accuracy.

Notes on the second drawtext:

  • drawtext=fontfile='/usr/share/fonts/urw-base35/C059-Bold.otf' defines the font to be used for the text.
  • fontcolor=yellow defines the color of the font of the text.
  • fontsize=$lowerFont defines the size of the font of the text.
  • x=(w-text_w)/2 defines the X-coordinate of the location for the text on the frame, here we center the text horizontally on the frame.
  • y=((h-text_h)/2)+$upperFont defines the Y-coordinate of the location for the text on the frame, here shift the text from the vertical center  of the frame.
  • text='Elapsed\: %{eif\:(t)\:d}.%{eif\:(mod(t, 1)*pow(10,$mantissaDigits))\:d\:$mantissaDigits}' We print the elapsed seconds since the video started with specific decimal digit accuracy.

Qubes OS 3.2: Resize fedora-23 TemplateVM Root Image 1

Recently, we needed to increase the size of the root image for the fedora-23 TemplateVM.
We had to do this as we wanted to install in /opt a few IDEs, including android-studio which takes a lot of space when accompanied by the Android SDK.

Following the excellent guide at, we did the following:

  1. Made sure that the fedora-23 TemplateVM and all VMs based on that template were shut down.
    This included stopping the sys-firewall and sys-net VMs as well (in this order).
  2. Then, in the VM Settings window at the Basic tab for the fedora-23 TemplateVM, we disabled the networking by selecting none on the NetVM: drop-down list and pressed OK to apply the settings changes.
  3. Following, in dom0 Terminal Emulator we run the following command:
    truncate -s 40G /var/lib/qubes/vm-templates/fedora-23/root.img;
  4. Afterwards we started the fedora-23 TemplateVM and run the following in the terminal:
    sudo resize2fs /dev/mapper/dmroot;
    Please note that if your output is Nothing to do! then most likely you forgot a VM that is based on the fedora-23 TemplateVM running. Normally your screen should print something along the lines of Resizing the filesystem...
  5. Next, we shut down the fedora-23 TemplateVM, and went to the VM Settings window to enable networking by selecting whatever we had there before (for us it was default (sys-firewall)).
  6. Finally, we could start using our VMs, their root.img were of the new extended size.

LibreOffice Calc: get the distinct/unique values in a column or a list of elements 1

These videos demonstrate how to get the distinct/unique values in a column or a list of elements in LibreOffice Calc.

Procedure to get the distinct values in a column or a list of elements:

  1. Select the column (or the list of data) that you want to process
  2. Click on the top menu Data
    then click on the option group More Filters
    and finally on the option Standard Filter...
  3. In the new window, change the Field Name on the first row to - none -
  4. Click on the Options label and enable the No duplications checkbox
  5. Finally press the OK button

Video demonstrating how to get the distinct values in a column:

Video demonstrating how to get the distinct values in a list of elements:

Practice Problem for Google Hash Code 2018

Happy new year people!!

Google released a practice problem for Google Hash Code 2018!

Please do not forget to register!

Practice Problem for Google Hash Code 2018 - Problem Statement (873 downloads)


Practice Problem for Google Hash Code 2018 - Data Sets (456 downloads)

Submission deadline: Thursday, Mar 1, 19:00 Cyprus time (18:00 CET)


Practice Problem for Hash Code


Did you know that at any given time, someone is cutting pizza somewhere around the world? The decision about how to cut the pizza sometimes is easy, but sometimes it’s really hard: you want just the right amount of tomatoes and mushrooms on each slice. If only there was a way to solve this problem using technology…

Problem description


The pizza is represented as a rectangular, 2-dimensional grid of R rows and C columns. The cells within the grid are referenced using a pair of 0-based coordinates [r, c] , denoting respectively the row and the column of the cell.

Each cell of the pizza contains either:

  • mushroom, represented in the input file as M ; or
  • tomato, represented in the input file as T


A slice of pizza is a rectangular section of the pizza delimited by two rows and two columns, without holes.
The slices we want to cut out must contain at least L cells of each ingredient (that is, at least L cells of mushroom and at least L cells of tomato) and at most H cells of any kind in total – surprising as it is, there is such a thing as too much pizza in one slice.

The slices being cut out cannot overlap. The slices being cut do not need to cover the entire pizza.


The goal is to cut correct slices out of the pizza maximizing the total number of cells in all slices.

Input data set

The input data is provided as a data set file – a plain text file containing exclusively ASCII characters with lines terminated with a single \n character at the end of each line (UNIX- style line endings).

File format

The file consists of:

  • one line containing the following natural numbers separated by single spaces:
    • R (1 ≤ R ≤ 1000) is the number of rows,
    • C (1 ≤ C ≤ 1000) is the number of columns,
    • L (1 ≤ L ≤ 1000) is the minimum number of each ingredient cells in a slice,
    • H (1 ≤ H ≤ 1000) is the maximum total number of cells of a slice
  • R lines describing the rows of the pizza (one after another). Each of these lines contains C
    characters describing the ingredients in the cells of the row (one cell after another). Each character is either M (for mushroom) or T (for tomato).

Example Input File

3 5 1 6

3 rows, 5 columns, min 1 ingredient per slice, max 6 cells per slice


File format

The file must consist of:

  • one line containing a single natural number S (0 ≤ S ≤ R × C) , representing the total number of slices to be cut,
  • U lines describing the slices. Each of these lines must contain the following natural numbers
    separated by single spaces:

    • r1 , c1 , r2 , c2 (0 ≤ r1, r2 < R, 0 ≤ c1, c2 < C)  describe a slice of pizza delimited by the rows r1 and r2 and the columns c1 and c2 , including the cells of the delimiting rows and columns. The rows ( r1 and r2 ) can be given in any order. The columns ( c1 and c2 ) can be given in any order too.


0 0 2 1
0 2 2 2
0 3 2 4

Example description

3 slices.
First slice between rows (0,2) and columns (0,1).
Second slice between rows (0,2) and columns (2,2).
Third slice between rows (0,2) and columns (3,4).

Slices described in the example submission file marked in green, orange and purple.


For the solution to be accepted:

  • the format of the file must match the description above,
  • each cell of the pizza must be included in at most one slice,
  • each slice must contain at least L cells of mushroom,
  • each slice must contain at least L cells of tomato,
  • total area of each slice must be at most H


The submission gets a score equal to the total number of cells in all slices.

Note that there are multiple data sets representing separate instances of the problem. The final
score for your team is the sum of your best scores on the individual data sets.

Scoring example

The example submission file given above cuts the slices of 6, 3 and 6 cells, earning 6 + 3 + 6 = 15 points.

Past editions

— From

Hash Code started in 2014 with just 200 participants from France. In 2017, more than 26,000 participants from across Europe, the Middle East and Africa took part in the competition. You can take a look at the problems and winning teams from past editions of Hash Code below.

Past problem statements

Router placement

Hash Code 2017, Final Round
Hash Code 2017, Final Round - Problem (401 downloads)
Who doesn’t love wireless Internet? Millions of people rely on it for productivity and fun in countless cafes, railway stations and public areas of all sorts. For many institutions, ensuring wireless Internet access is now almost as important a feature of building facilities as the access to water and electricity. Typically, buildings are connected to the Internet using a fiber backbone. In order to provide wireless Internet access, wireless routers are placed around the building and connected using fiber cables to the backbone. The larger and more complex the building, the harder it is to pick router locations and decide how to lay down the connecting cables.

Streaming videos

Hash Code 2017, Online Qualification Round
Hash Code 2017, Online Qualification Round - Problem (475 downloads)
Have you ever wondered what happens behind the scenes when you watch a YouTube video? As more and more people watch online videos (and as the size of these videos increases), it is critical that video-serving infrastructure is optimized to handle requests reliably and quickly. This typically involves putting in place cache servers, which store copies of popular videos. When a user request for a particular video arrives, it can be handled by a cache server close to the user, rather than by a remote data center thousands of kilometers away. Given a description of cache servers, network endpoints and videos, along with predicted requests for individual videos, decide which videos to put in which cache server in order to minimize the average waiting time for all requests.

Schedule Satellite Operations

Hash Code 2016, Final Round
Hash Code 2016, Final Round - Problem (449 downloads)
A satellite equipped with a high-resolution camera can be an excellent source of geo imagery. While harder to deploy than a plane or a Street View car, a satellite — once launched — provides a continuous stream of fresh data. Terra Bella is a division within Google that deploys and manages high-resolution imaging satellites in order to capture rapidly-updated imagery and analyze them for commercial customers. With a growing constellation of satellites and a constant need for fresh imagery, distributing the work between the satellites is a major challenge. Given a set of imaging satellites and a list of image collections ordered by customers, schedule satellite operations so that the total value of delivered image collections is as high as possible.

Optimize Drone Deliveries

Hash Code 2016, Online Qualification Round
Hash Code 2016, Online Qualification Round - Problem (485 downloads)
The Internet has profoundly changed the way we buy things, but the online shopping of today is likely not the end of that change; after each purchase we still need to wait multiple days for physical goods to be carried to our doorstep. Given a fleet of drones, a list of customer orders and availability of the individual products in warehouses, schedule the drone operations so that the orders are completed as soon as possible.

Route Loon Balloons

Hash Code 2015, Final Round
Hash Code 2015, Final Round - Problem (304 downloads)
Project Loon aims to bring universal Internet access using a fleet of high altitude balloons equipped with LTE transmitters. Circulating around the world, Loon balloons deliver Internet access in areas that lack conventional means of Internet connectivity. Given the wind data at different altitudes, plan altitude adjustments for a fleet of balloons to provide Internet coverage to select locations.

Optimize a Data Center

Hash Code 2015, Online Qualification Round
Hash Code 2015, Online Qualification Round - Problem (512 downloads)
For over ten years, Google has been building data centers of its own design, deploying thousands of machines in locations around the globe. In each of these of locations, batteries of servers are at work around the clock, running services we use every day, from Google Search and YouTube to the Judge System of Hash Code. Given a schema of a data center and a list of available servers, your task is to optimize the layout of the data center to maximize its availability.

Street View Routing

Hash Code 2014, Final Round
Hash Code 2014, Final Round - Problem (435 downloads)
The Street View imagery available in Google Maps is captured using specialized vehicles called Street View cars. These cars carry multiple cameras capturing pictures as the car moves around a city. Capturing the imagery of a city poses an optimization problem: the fleet of cars is available for a limited amount of time and we want to cover as much of the city streets as possible.

Google Hash Code 2018 Limassol Cyprus – Call for participation

We’ll be hosting a hub at the Cyprus University of Technology for the Online Qualification Round of Hash Code, a team-based programming competition created by Google for university students and industry professionals. The Online Qualification Round takes place on the 1st of March at 19:30 EET and registered teams from Cyprus are invited to participate from our hub, which will be at the Labs of the University. Top scoring teams from the Online Qualification Round will then be invited to Google’s Paris office to compete in the Final Round of the competition on the 1st of April.

If you’re interested in joining our hub, find a team (two to four people) and register at Make sure to select Cyprus University of Technology from the list of hubs in the Judge System.

For more information about this and other hubs in Cyprus (including the twin event in Nicosia) visit

Hash Code 2018 Limassol Cyprus – Facebook Event



Cyprus University of Technology
Room: ΚΧΕ 1 - Computer Lab
Polyxeni Loizia and Eleni Autonomou Building (Old Cadastre)
Athinon Street

Τεχνολογικό Πανεπιστήμιο Κύπρου
Δωμάτιο: ΚΧΕ 1 -  Εργαστήριο Ηλεκτρονικών Υπολογιστών
Κτήριο Πολυξένη Λοϊζία και Ελένη Αυτονόμου (Παλιό Κτηματολόγιο)
Οδός Αθηνών

Date and Time:

1st March 2018
From: 19:30 EET
To: 23:30 EET

Free Amenities Offered

High speed Internet access
Wi-Fi access to the Internet for your mobile devices (personal computers and smart phones)
Lab computers will be available for use by the participants
Food in the form of snacks and beverages will be available outside the labs

Google Hash Code 2018 – Online Qualification Round Schedule

18:30 EET:

  • The hub will open to the public
  • People can view the live stream on the video projector
  • Teams can set themselves up with the help of the volunteers

19:30 EET:

  • Live stream starts

19:45 EET:

  • Task will be made available, competition starts
  • Scoreboard will be displayed on the video projector
  • Participating teams will be confirmed in the Judge System

23:30 EET:

  • End of the competition
  • Announcement of the score for the local teams

00:00 EET:

  • The hub will close