Monthly Archives: January 2021

Programming Course Series [01 – Introductory course to python]

Computer programming is important today because so much of our world is automated. Humans need to be able to control the interaction between people and machines. Since computers and machines are able to do things so efficiently and accurately, we use computer programming to harness that computing power.

This is the first of hopefully many programming courses that can introduce technically inclined people to Python programming.

  Date and Time


Information on our VPN service (instructions for iOS devices) will be provided to the registrants that cannot join us along with instructions on our BigBlueButton platform.




George Michael


Everybody can write a computer program (An introduction using Python)


Introduction to programming and reasons to write programs?

These are the course-wide materials as well as Introductions’ first section where we discuss what writing programs mean. In the third part of the class, we will finish the Introduction and have the quiz and first task.

Installing and Using Python

We’re going to set up stuff so that you can write Python programs.

Introduction to programming and reasons to write programs? (continued)

We try to cover the “big picture” of programming so that you get a “table of contents” from what to expect to learn. Don’t worry if, the first time you hear it, not everything makes perfect sense. This part is very broad.

Variables and Expressions

We will explain how a program uses the memory of the machine to store, retrieve and process information in this section.

Conditional Code

We will move from sequential code in this section that simply runs one line of code after another to conditional code where some steps are skipped. It is a very basic idea – but it is how “choices” are made by computer software.


We are going to learn about what functions are and how we can use them. Functions will be an essential way for us to make sense of our code, as we move into more and more complicated programs.

Loops and Iteration

Our four fundamental programming patterns are completed by loops and iteration. Loops are the way we say Python over and over to do something. Loops are the manner in which we create programs that remain with a problem until the problem is solved.

Using Nomenclature in TeXstudio

Recently, we were compiling a Latex document that was using the nomencl package to create a nomenclature list. The tool that we were using was TeXstudio. We noticed that the nomenclature was not in the final document and no error was generated to indicate so.

To fix the issue, we had to manually execute the makeindex command which would create the necessary meta-files. To avoid using a terminal each time we wanted to update the nomenclature, we defined a custom command in TeXstudio which would make the process a bit more easy for us.

In the following video you will see the following steps:

  1. Going to Options menu.
  2. From there selecting the Configure TeXstudio option.
  3. From the popup window, we switched to the Build tab by clicking on the appropriate button on the left side column.
  4. In the group User Commands we clicke on the + Add button which created a new entry for us.
  5. In the new entry we filled:
    1. The menu name of the command: user0: Make Nomenclature
    2. The actual command to build the files needed for the nomenclature: makeindex -s -t %.nlg -o %.nls %.nlo
  6. Then we clicked on the OK button to close that window.
  7. To test that the command works as expected, we went to the Tools menu.
  8. From there to the sub-menu named User, where we found our new command listed as 1: Make Nomenclature.
    This command produced all files necessary for the makenomenclature command to work.
  9. Finally, we clicked on the Build & View button to verify that everything is OK.

Cloudflare Origin Server Certificate for IIS 10 Server on Windows Server 2016 to allow Full (strict) mode SSL/TLS encryption mode 2

Create a Certificate Request from your Windows Server

  1. Open Internet Information Services (IIS) Manager from the Windows Server 2016 through Control Panel -> Administrative Tools
  2. Select your server from the Connections and open Server Certificates
  1. From the Server Certificates Actions select Create Certificate Request
  1. Fill in the following form with your details:
Common name: [your domain]
Organization: [your organization name]
  1. Set the settings for the Cryptographic service provider of the certificate, the bigger the length of the certificate the better the security but it makes the server slower.
  1. Specify the filename of the txt file where you will save the certificate request

Create the certificate from Cloudflare using your own certificate request that you created from your Windows Server

  1. Open your Cloudflare account, select your domain, open SSL/TLS tab and click on Origin Server in order to create the certificate
  1. Select the option ‘I have my own private key and CSR’ where you will Copy-Paste the certificate you saved on the txt file from your Windows Server, fill in the hostnames, select the expiration years and press Next
  1. Copy-Paste in PEM key format the certificate in a text file and save the file

Add the public certificate from Cloudflare at your Windows Server

  1. Copy the file with the PEM certificate from Cloudflare at your Windows Server
  2. Select ‘Complete Certificate Request’ from the IIS Manager Server Certificates Actions
  1. Select the PEM certificate you copied at the server and add a friendly name (e.g. the domain it covers and the expiration date of it):
  1. The certificate will appear at the list of the Server Certificates with the Friendly name you added at the form before

Import Cloudflare Origin CA root certificate at your Windows server

  1. Copy the Cloudflare Origin CA — RSA Root certificate from Cloudflare website, save to a file and transfer it to your Windows Server
  2. Open the Certificates Microsoft Management Console (MMC) snap-in by typing mmc.exe at the command prompt (or at the run dialog that you can open by pressing the buttons Win+R)
  3. On the File menu, select Add/Remove Snap-in
  1. In the Add or Remove Snap-ins dialog box, select Certificates snap-in in the Available snap-ins list, click Add, and then select OK
  1. In the Certificates snap-in dialog-box, select Computer account, and then select Next
  1. In the Select computer dialog box, click on Finish
  1. In the Add or Remove Snap-ins dialog box, select OK
  1. In the Certificates MMC snap-in, expand Certificates, right-click Intermediate Certification Authorities, point to All Tasks, and then select Import
  1. In the Certificate Import Wizard, select Next
  1. In the File to Import page, select the file with the Cloudflare origin CA root certificate you saved before, and then select Next
  1. Select Next at the Certificate Import Wizard
  1. Select Finish at the Certificate Import Wizard
  1. The certificate will appear at the Certificates list

Use the newly created server origin certificate from Cloudflare for your website

  1. Select Bindings from the IIS Manager Web Site Actions
  1. Select the https binding and click Edit. If you do not have an https binding, press Add... to create one like in the second screen down
  1. At the SSL certificate dropdown list Select the new certificate and press OK

Force your website domain to pass through Cloudflare

  1. Open your Cloudflare account, select your domain, go to DNS option and change the Proxy status for your website from DNS only to Proxied by click it
  1. Enable Cloudflare full (strict) SSL TLS encryption mode in the SSL/TLS tab

Google Hash Code 2021 – Practice Problem 1

Even more pizza

Hash Code 2021, Practice Round - Problem (1871 downloads)

Online Qualification Round Problem and Input Data Set

Hash Code 2021, Online Qualification Round – Problem (297 downloads)

World Finals Problem and Input Data Set

Hash Code 2021, Final Round – Problem (10 downloads)


Isn’t it fun to share pizza with friends? But, sometimes you just don’t have enough time to choose what pizza to order. Wouldn’t it be nice if someone else chose for you?

In an imaginary world…

Problem description


Help the imaginary pizzeria choose the pizzas to deliver to Hash Code teams. And since we want everyone to enjoy their food, let’s try to deliver to each team, as many different ingredients as we can.


Expecting many hungry customers, the pizzeria has already prepared some pizzas with different ingredients. Each pizza can be delivered to at most one team. There can be multiple pizzas with the exact same set of ingredients.

For example , there are 5 pizzas available in the pizzeria:

Pizza 0: onion, pepper, olive
Pizza 1: mushroom, tomato, basil
Pizza 2: chicken, mushroom, pepper
Pizza 3: tomato, mushroom, basil
Pizza 4: chicken, basil

Note that Pizzas 1 and 3 have the same ingredients, even though they are mentioned in different order.


Teams of 2, 3, or 4 people all ordered pizzas. Each team ordered one pizza per team member, but did not specify what ingredients to put on the pizzas. The pizzeria might not deliver to a team (no pizzas are sent to that team). However, if the order is delivered, exactly one pizza should be available per person. For example, it is an error to send 3 pizzas to a 4-person team.


Given the description of the pizzas available, and the number of teams of 2, 3, or 4 people that have ordered, decide which pizzas to send to each of the teams. The goal is to maximize, per team, the number of different ingredients used in all their pizzas.

For example , if we deliver to a 3-person team Pizzas 0, 2 and 3, there will be 7 different ingredients (9 ingredients in total, but pepper and mushroom occur twice):

  • Pizza 0
    • onion
    • pepper
    • olive
  • Pizza 2:
    • chicken
    • mushroom
    • pepper (is already on Pizza 0)
  • Pizza 3:
    • tomato
    • mushroom (is already on Pizza 2)
    • basil

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 (UNIX- style line endings).

File format

The first line of the input file contains the following integer numbers separated by single spaces:

  • M ( 1 ≤ M ≤ 100,000 ) – the number of pizzas available in the pizzeria
  • T2 ( 0 ≤ T2 ≤ 50,000 ) – the number of 2-person teams
  • T3 ( 0 ≤ T3 ≤ 50,000 ) – the number of 3-person teams
  • T4 ( 0 ≤ T4 ≤ 50,000 ) – the number of 4-person teams

The next M lines describe the pizzas available. Each line contains (space separated):

  • an integer I ( 1 ≤ I ≤ 10,000 ) – the number of ingredients,
  • followed by the list of I ingredients – Each ingredient consists of lowercase ASCII letters and dash (-) characters, and its length can be between 1 and 20 characters in total. Each ingredient in a pizza is different, but the same ingredient can appear on different pizzas.


Input file
5 1 2 1
3 onion pepper olive
3 mushroom tomato basil
3 chicken mushroom pepper
3 tomato mushroom basil
2 chicken basil
5 pizzas, 1 team of two, 2 teams of three, and 1 team of four
Pizza 0 has the given 3 ingredients
Pizza 1 has the given 3 ingredients
Pizza 2 has the given 3 ingredients
Pizza 3 has the given 3 ingredients
Pizza 2 has the given 2 ingredients


File format

The first line of the submission file contains a number D ( 1 ≤ D ≤ T2 + T3 + T4 ), representing the number of pizza deliveries.

The following D lines contain descriptions of each delivery. Each line contains the following integer numbers separated by single spaces:

  • L ( 2 ≤ L ≤ 4 ) – the number of people in the team
  • followed by the list of pizzas, P1 … PL – the space separated indexes of the pizzas delivered to that team

Even though it’s nice to deliver pizzas to all teams, it is allowed to make fewer deliveries than the number of teams. However, making more deliveries than the number of teams is an error. It is also an error to make more deliveries to 2, 3 or 4-person teams than the corresponding number
of teams provided in the input file: the number of lines with L=N, should not be greater than TN.


Submission file
2 1 4
3 0 2 3
Pizzas are delivered to 2 teams
A 2-person team will receive Pizza 1 and Pizza 4
A 3-person team will receive Pizza 0, Pizza 2 and Pizza 3


In order for the submission to be accepted:

  • each pizza must be part of at most one order,
  • for all N-person teams, either nobody or everybody receives a pizza,
  • there are TN or less deliveries to teams of N people.


For each delivery, the delivery score is the square of the total number of different ingredients of all the pizzas in the delivery. The total score is the sum of the scores for all deliveries.

For example , with the example input file and the example submission file above, there are

  • 4 ingredients delivered to the two-person team (mushroom, tomato, basil, chicken). The score for that team is 42 = 16
  • 7 ingredients delivered to the tree-person team. The score for that team is 72 = 49.
  • (The score is 0 for the two teams that didn’t have their order delivered)

The total score is 16 + 49 = 65 .

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

Past editions

— From

Hash Code started in 2014 with just 200 participants from France. In 2020, more than 100,000 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

Traffic Signaling

Hash Code 2021, Online Qualification Round
Hash Code 2021, Online Qualification Round – Problem (297 downloads)
Given the description of a city plan and planned paths for all cars in that city, optimize the schedule of traffic lights to minimize the total amount of time spent in traffic, and help as many cars as possible reach their destination before a given deadline.

Assembling smartphones

Hash Code 2020, Final Round
Hash Code 2020, Final Round - Problem (570 downloads)
In this problem statement, we will explore the idea of operating an automated assembly line for smart phones.
Building a smart phone is a complex process that involves assembling numerous components, including the screen, multiple cameras, microphones, speakers, a processing unit, and a storage unit.
In order to automate the building of a smart phone, we will be using robotic arms that can move around the assembly workspace performing all necessary tasks.

Book scanning

Hash Code 2020, Online Qualification Round
Hash Code 2020, Online Qualification Round - Problem (567 downloads)
Books allow us to discover fantasy worlds and better understand the world we live in. They enable us to learn about everything from photography to compilers… and of course a good book is a great way to relax!
Google Books is a project that embraces the value books bring to our daily lives. It aspires to bring the world’s books online and make them accessible to everyone. In the last 15 years, Google Books has collected digital copies of 40 million books in more than 400 languages , partly by scanning books from libraries and publishers all around the world.
In this competition problem, we will explore the challenges of setting up a scanning process for millions of books stored in libraries around the world and having them scanned at a scanning facility.

Compiling Google

Hash Code 2019, Final Round
Hash Code 2019, Final Round - Problem (480 downloads)
Google has a large codebase, containing billions of lines of code across millions of source files. From these source files, many more compiled files are produced, and some compiled files are then used to produce further compiled files, and so on.
Given then huge number of files, compiling them on a single server would take a long time. To speed it up, Google distributes the compilation steps across multiple servers.
In this problem, we will explore how to effectively use multiple compilation servers to optimize compilation time.

Photo slideshow

Hash Code 2019, Online Qualification Round
Hash Code 2019, Online Qualification Round - Problem (449 downloads)
As the saying goes, “a picture is worth a thousand words.” We agree – photos are an important part of contemporary digital and cultural life. Approximately 2.5 billion people around the world carry a camera – in the form of a smart phone – in their pocket every day. We tend to make good use of it, too, taking more photos than ever (back in 2017, Google Photos announced it was backing up more than 1.2 billion photos and videos per day).
The rise of digital photography creates an interesting challenge: what should we do with all of these photos? In this competition problem, we will explore the idea of composing a slideshow out of a photo collection.

City Plan

Hash Code 2018, Final Round
Hash Code 2018, Final Round - Problem (470 downloads)
The population of the world is growing and becoming increasingly concentrated in cities. According to the World Bank, global urbanization (the percentage of the world’s population that lives in cities) crossed 50% in 2008 and reached 54% in 2016.
The growth of urban areas creates interesting architectural challenges. How can city planners make efficient use of urban space? How should residential needs be balanced with access to public utilities, such as schools and parks?

Self-driving rides

Hash Code 2018, Online Qualification Round
Hash Code 2018, Online Qualification Round - Problem (443 downloads)
Millions of people commute by car every day; for example, to school or to their workplace.
Self-driving vehicles are an exciting development for transportation. They aim to make traveling by car safer and more available while also saving commuters time.
In this competition problem, we’ll be looking at how a fleet of self-driving vehicles can efficiently get commuters to their destinations in a simulated city.

Router placement

Hash Code 2017, Final Round
Hash Code 2017, Final Round - Problem (1408 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 (1396 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 (1052 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 (1174 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 (891 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 (1194 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 (1079 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.

Package pdftex.def Error: File `xyz-eps-converted-to.pdf’ not found: using draft setting. [Ubuntu]

Recently we were struggling with the following error whenever we were trying to use an eps figure with the pdflatex compiler.

Package pdftex.def Error: File `xyz-eps-converted-to.pdf' not found: using draft setting.

After trying several online remedies which all failed, we tried to convert the eps figure to pdf manually on the shell and we got the following error:

$ epstopdf
Command 'epstopdf' not found, but can be installed with:
sudo apt install texlive-font-utils

Following the advice on the shell, we installed texlive-font-utils and guess what? After compiling our Latex document again, the error was gone and the eps figure was successfully converted to a pdf!!