https://github.com/jm1/code-cracker-curriculum-2020

Advent calendar 2020 for my lovely wife, Mareike.
https://github.com/jm1/code-cracker-curriculum-2020

Last synced: 5 months ago
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Advent calendar 2020 for my lovely wife, Mareike.

Host: GitHub
URL: https://github.com/jm1/code-cracker-curriculum-2020
Owner: JM1
Created: 2020-11-16T13:13:23.000Z (over 5 years ago)
Default Branch: master
Last Pushed: 2020-12-18T09:21:32.000Z (over 5 years ago)
Last Synced: 2025-05-25T00:19:20.059Z (about 1 year ago)
Language: Makefile
Homepage:
Size: 71.3 KB
Stars: 0
Watchers: 1
Forks: 0
Open Issues: 0
Metadata Files:
- Readme: README.md

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README

# Code Cracker Curriculum (CCC) 2020

To my lovely wife, Mareike.

Welcome to your advent calender 2020 🎅
This year's edition is going to be different, it's special, so thrilling, you will lovin' it...
But wait, what the f***? 😮

A filthy little mobster 👻 has stolen all of your sweets and hid them all over our house!😱
But do not despair! 😎

Being a wannabe prankster😝, he left behind a series of code puzzles.
Each puzzle consists of a tiny programming exercise that, once solved,
will reveal a secret that leads to the location of your daily sweets 🍬🍭🍫

Apparently, this jerk wasn't very clever nor cautious, as he left traces and hints everywhere.
And, as the last resort, you can always ask your fella 👨💍, of course.
But beware: Cheating won’t help in the long run, because the course
difficulty might adapted dynamically to match your progress 😉

I hope you will enjoy your little journey into the world of coding.
It will require your investigative intuition, combinatory ability and analytic skills 👮‍
But you wanted to learn Python anyway, didn't you? 😉

So let the games begin!

## 2020-12-01, Tuesday, Day 0: Warmup

As every good detective 👮‍, before following traces and hunting down wrongdoers 😈,
you have to setup your working environment first. Our ultimate goal is to find all sweets,
hence we need tools that keeps us focussed on cracking the secrets. No muss, no fuss.

From your fellow data scientist you've heard of [Python 🐍](https://www.manning.com/books/get-programming),
a very popular programming language to get things done.
So let us start!

First, download and install Python 3 and a suitable [IDE](https://wiki.python.org/moin/IntegratedDevelopmentEnvironments)
for Python development on Windows 10.

Examples:
* [`Spyder IDE`](https://docs.anaconda.com/anaconda/user-guide/tasks/integration/spyder/)
bundled with [Anaconda](https://www.anaconda.com/products/individual) (⚠️Recommended⚠️)

*NOTE*:
> [`Spyder IDE`](https://www.spyder-ide.org/) is pre-installed in
> [Anaconda Navigator](https://docs.anaconda.com/anaconda/navigator/),
> which is included in [Anaconda](https://www.anaconda.com/products/individual).
> On the Navigator Home tab, click the Spyder icon.

Free and open source under MIT license.

* [PyDev](https://www.pydev.org/)

Python IDE for Eclipse.
Free and open source under [Eclipse Public License](https://www.eclipse.org/legal/epl-v10.html).

> The recommended way of using PyDev is bundled in [LiClipse](http://www.liclipse.com/).

* [Sublime Text 3](https://www.sublimetext.com/3) and
[install its Python package](https://howtodoinjava.com/python/python-basics/install-python-sublime-editor/)

> Sublime Text may be downloaded and evaluated for free, however a license
> must be purchased for continued use. There is currently no enforced time
> limit for the evaluation.

Next, fetch [Python script `secret.py`](https://berrendorf.inf.h-brs.de/~jmeng2m/ccc2020/day01/secret.py),
open it with your newly installed IDE and hit `RUN`.
That's it for today! Easy start, wasn't it? 😘

## 2020-12-02, Wednesday, Day Ⅰ: Security through Obscurity

Our favorite villain left us a cryptic message: `QXVmIGRlciBNYXRyYXR6ZSB1bnRlciBkZW0gQmV0dCBpbSBEYWNoZ2VzY2hvc3MK`

This string looks like being [Base64](https://www.geeksforgeeks.org/base64-b64encode-in-python/) encoded.
Good for you! Obviously, the mystery-monger did not know that decoding is not encryption and that you
can easily reconstruct the secret by just decoding the base64 string! 🐧

Hints:
> Use Python's [base64](https://docs.python.org/3/library/base64.html) library to decode the secret!

Lines of Code (excl. blank lines): ~3

## 2020-12-03, Thursday, Day Ⅱ: World wide investigations

Our jester detected his shortcomings in security and has moved his secrets into the cloud 🌎
As if that would save him...

Download file [`secret.txt`](https://berrendorf.inf.h-brs.de/~jmeng2m/ccc2020/day03/secret.txt) using Python
and `print` its context.

Hints:
> Do not even think about using a browser to download that file, it won't work 😉

> You might use the [`Requests`](https://requests.readthedocs.io/en/master/) module for fetching content via HTTP.

> To install additional Python packages, follow install steps for your IDE, e.g.:
> * [Anaconda](https://docs.anaconda.com/anaconda/user-guide/tasks/install-packages/)
> * Standalone [Spyder IDE](https://miamioh.instructure.com/courses/38817/pages/downloading-and-installing-packages)
(Try [Anaconda](https://docs.anaconda.com/anaconda/user-guide/tasks/install-packages/) first!)
> * [PyDev](https://www.planetofbits.com/python/how-to-install-a-python-package-in-eclipse/)
> * Use [PIP](https://matthewhorne.me/how-to-install-python-and-pip-on-windows-10/), e.g.
`python -m pip install requests`

Lines of Code (excl. blank lines): ~3-10

## 2020-12-04, Friday, Day Ⅲ: Bridging worlds

It's friday and it looks like our stupid buddy is already becoming lazy. One man's loss is another woman's gain 😁

Download file [`secret_base64.txt`](https://berrendorf.inf.h-brs.de/~jmeng2m/ccc2020/day04/secret_base64.txt),
decode its context and print the results!

Hints:
> Combine your programs from the last two days!

Lines of Code (excl. blank lines): ~4-10

## 2020-12-05, Saturday, Day Ⅳ: Soul split and retrieval

The horcrux.. ehm.. secret has been cutted into 3 pieces!
Download [all files from here](https://berrendorf.inf.h-brs.de/~jmeng2m/ccc2020/day05/) and reconstruct the secret.

Hints:
> Reconstruction requires you to fetch and merge all strings. Doing so does not necessarily imply
> [loops](https://www.learnpython.org/en/Loops), although mastering loops might come in handy soon.

> It is not necessary to parse the site or its HTML code in Python, just manually
> search the site for links to files and then download these links within Python!

Lines of Code (excl. blank lines): ~8-10

## 2020-12-06, Sunday, Day ᚏ: 🍟🍗🍸

Damn, what a slaughterhouse 🔪⛑🌹🌷
It looks like this lunatic worked more thoroughly this time:
Our daily secret has been splitted into dozens of pieces!
Download [all files from here](https://berrendorf.inf.h-brs.de/~jmeng2m/ccc2020/day06/) and reconstruct the secret!

Hints:
> Do use [loops](https://www.learnpython.org/en/Loops).

> It is not necessary to parse the site or its HTML code in Python, just manually
> search the site for links to files, look for repeating pattern(s) within the urls,
> write a loop to generate the urls in Python and then download these urls with Python!

Lines of Code (excl. blank lines): ~8-10

## 2020-12-07, Monday, Day `b0110`: вєωαяє, ι αм ƒαη¢у!

You got mail! But.. (⊙_☉) ..wtf?

```Python
#!/usr/bin/env python3
# -*- coding: utf-8 -*-

secret = r'''
UEsDBBQACAgIANtKeVEAAAAAAAAAAAAAAAALAAAAX3JlbHMvLnJlbHOtkk1LA0EMhu/9FUPu3Wwr
iMjO9iJCbyL1B4SZ7O7Qzgczaa3/3kEKulCKoMe8efPwHNJtzv6gTpyLi0HDqmlBcTDRujBqeNs9
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SnlRAAAAAAAAAAAAAAAAEAAAAGRvY1Byb3BzL2FwcC54bWydkc1uwyAQhO99CgvlGmNHqWVFmKg/
6ilSI9VterMobGwqGxBsouTtS5rK8bm3HWb0DSxsfRr65Ag+aGsqkqcZScBIq7RpK/Jev8xLkgQU
RoneGqjIGQJZ8zu29daBRw0hiQQTKtIhuhWlQXYwiJBG20Rnb/0gMErfUrvfawnPVh4GMEgXWVZQ
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eCEx/gZfxtRETqydxu7NCRkBy3IamhixyYvWC9f91Y0qinHR/AdQSwcIhXVYOSABAAD+AQAAUEsD
BBQACAgIANtKeVEAAAAAAAAAAAAAAAARAAAAZG9jUHJvcHMvY29yZS54bWyNUsFuwjAMve8rqtzb
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cmQvX3JlbHMvZG9jdW1lbnQueG1sLnJlbHOtkU0KwjAQhfeeIszeplUQkaZuRHAr9QAxnbbBNgnJ
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hqpAk79yvdnpwOU3UEsHCLHkBm4nAQAAwgMAAFBLAwQUAAgICADbSnlRAAAAAAAAAAAAAAAAEQAA
AHdvcmQvZG9jdW1lbnQueG1srVVLbtswEN33FALXTSQ1HzhC5KCtmzZAGxhwujZoipII84chZcc9
SXa9SHa5UI/QofVxmqCF0WQjSpyZ994MZ6jzi1sloxUHJ4zOSXqYkIhrZgqhq5x8v7k8GJHIeaoL
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qygsGxsqZvFEF0IKv9kmvhOVHr9M1dOa/R9e6B/FsqtKG6ALiYOAQFFQR8Y4CwtTbMJqt48pbJeZ
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H5d49w8Z/wZQSwcIpx56m2kCAACIBgAAUEsDBBQACAgIANtKeVEAAAAAAAAAAAAAAAAPAAAAd29y
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47nLtOS9q5F3jJs649Xq9erOv6Y8V9PU8WGUmDvrxnn583iN2NBT7nA70459TQ0dG6pLn08wXeWe
HiekCLJIWkFbSwOHGn9dBrHjlzN6I/WYEsq0mdPaqjcXNdC7rQTnbl6w0pVo12T4/ZQtjCG3jCLk
X2SXThIebIvfufXEaDAbJZwA6NGShzU1NJRoynhgIAN3z8ET0/cZ08KCcWNt0CevFZ1K3KB5Y1nQ
e9NOqOgn/Qi8S/AlGY86ZDz6FzUWzK2Kca7yWeTNLyrR8LIgUnAJ32o/A0N7NohL9f0hWeL5GcsH
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AwQUAAgICADbSnlRAAAAAAAAAAAAAAAAEwAAAFtDb250ZW50X1R5cGVzXS54bWy9VDlPwzAU3vsr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'''
```

To make sense of this pile of byte junk,
you have to `base64`-decode variable `secret`
and write its contents to a `*.docx` file.
Open this `*.docx` file in Word!

Hints:
> No further processing is required, just decode and write to disk.

> Use [Python's `with` statement](https://www.pythonforbeginners.com/files/with-statement-in-python),
> because it will automatically close the file.

Lines of Code (excl. blank lines): ~5-8

## 2020-12-08, Tuesday, Day `b0111`: `¯\(°_o)/¯`

You found a link:
[`mysterious_hint.txt`](https://berrendorf.inf.h-brs.de/~jmeng2m/ccc2020/day08/mysterious_hint.txt).
What now, Miss Marple?

Hints:
> 🌎📥🚪🔑📨

> You may use the `IPython Console`, which e.g. comes preinstalled with
> [`Spyder IDE`](http://docs.spyder-ide.org/develop/current/ipythonconsole.html),
> to execute and visualize Python code interactively.
> (`Spyder IDE` is bundled with [`Anaconda`](https://docs.anaconda.com/anaconda/user-guide/tasks/integration/spyder/))

Lines of Code (excl. blank lines): ~8-10

## 2020-12-09, Wednesday, Day `b1000`: High priestess of the Temple of Apollo

Our cheeky rascal did not leave any trace today. Hmm..
Let us consult [Pythia](https://en.wikipedia.org/wiki/Pythia) aka the Oracle of Delphi!

Send your `{'question': 'Where to find today\'s suprise?'}` using `HTTP POST` to
[`the oracle`](https://berrendorf.inf.h-brs.de/~jmeng2m/ccc2020/day09/oracle) and
`print` the serve..eh..oracle's response!

Hints:
> Note, nowadays Pythia is speaking Python only, no ancient greek nor modern browser'ish!

> Making a request with [`Requests`](https://requests.readthedocs.io/en/master/user/quickstart/) is very simple.

Lines of Code (excl. blank lines): ~3-5

## 2020-12-10, Thursday, Day `b1001`: Swarm intelligence

Detective 👮‍, we found five individuals that witnessed how our criminal tried to hide his loot.
Due to the corona situation, we'll have to do the questioning of the witnesses remotely.

Send your `{'question': 'What did you see?'}` using `HTTP POST` to
[all witnesses](https://berrendorf.inf.h-brs.de/~jmeng2m/ccc2020/day10/),
fetch their responses and `print` your conclusion on this case.

Hints:
> You may combine your findings from Saturday and yesterday.

Lines of Code (excl. blank lines): ~8-10

## 2020-12-11, Friday, Day X: Cold cases

We have to go through the [archive](https://berrendorf.inf.h-brs.de/~jmeng2m/ccc2020/day11/) and
search all previous cases to find hints about where our kidnap victim (🍬) might have been taken to.

Go `get` and `print` all criminal records, there must be something that leads us to today's crime scene!

Hints:
> Use `HTTP GET`, no `HTTP POST` required.

> Note, for security reasons access to our logs is granted via Python only. Browser access has been disabled!

Lines of Code (excl. blank lines): ~10-15

## 2020-12-12, Saturday, Day B: Career Advancement

Your combinatory proficiency and programming skills have been recognized by the federal intelligence service 🔫😎.
You have been asked to help with a mysterious message that was received from unknown origin.

```Python
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
cipher = [' ', ' ', ' ', ' ', ' ', ' ', 'a', 'a', 'b', 'c',
'c', 'd', 'd', 'e', 'e', 'e', 'e', 'e', 'e', 'e',
'e', 'h', 'h', 'i', 'i', 'i', 'l', 'l', 'm', 'n',
'n', 'n', 'n', 'r', 'r', 'r', 's', 't', 't', 't', 't']
lookup_table = ( 2, 6, 16, 20, 24, 31, 10, 33, 32, 8,
11, 3, 21, 4, 14, 22, 26, 27, 29, 36,
39, 9, 12, 0, 18, 38, 15, 25, 17, 1,
23, 30, 40, 5, 28, 37, 7, 13, 19, 34, 35)
```

Hints:
> No coding required! Use Pen and paper.

> Zero-based numbering, i.e. initial element of a sequence is assigned the index 0, rather than the index 1!

Lines of Code (excl. blank lines): 0

## 2020-12-13, Sunday, Day C: First day at Bletchley Park

You have been asked to decipher yet another cryptic message:
```Python
cipher = [ 8, 13, 30, 3, 4,
17, 30, 10, 11, 4,
8, 13, 4, 13, 30,
15, 5, 0, 13, 13,
4, 30, 27, 1, 4,
17, 30, 3, 4, 12,
30, 10, 27, 7, 11,
18, 2, 7, 17, 0,
13, 10, 30, 8, 13,
30, 3, 4, 17, 30,
10, 27, 2, 7, 4 ]
```
Which secret might be concealed within this cryptic message?!?

Ma'am, we just got a call from London!
Our spies found a blueprint of the Enigma machine that was used to encrypt the above's secret:

```Python
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# TOP SECRET

cleartext = 'classified information example'.lower()

# 0 1 2 3 4 5 6 7 8 9 10
abc = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k',
# 11 12 13 14 15 16 17 18 19 20 21
'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
# 22 23 24 25 26 27 28 29 30 31 32
'w', 'x', 'y', 'z', 'ö', 'ü', 'ä', 'ß', ' ', ',', '-']

cipher = []
for c in cleartext:
idx = abc.index(c)
cipher.append(idx)

print(cipher)
```

Find out how this encryption machine works.
Manually apply all steps in reverse order to decrypt today's location in cleartext!

Hints:

> No coding required!
> Step through the code line by line to understand its internals.
> Lookup unknown function in the Python documentation,
> e.g. [More on Lists](https://docs.python.org/3/tutorial/datastructures.html#more-on-lists).
> Use pen and paper to track all variables inside and outside of the loop in a
> [table of values](https://de.wikipedia.org/wiki/Wertetabelle).
> Once you got an idea of the code, develop an inverse algorithm in pseudo code on paper,
> that rewinds all changes and recovers the original input!

> It is strongly recommended to use a debugger! This allows one to add breakpoints at arbitrary lines of code at which
> the program's execution flow will be interrupted, so that e.g. variable values at the current loop iteration can be
> inspected. [Spyder GUI has a debugger built-in](https://docs.spyder-ide.org/current/debugging.html).

> IF YOU'RE STUCK, THEN ASK YOUR CHIEF SCIENTIST NEXT DOOR!!!

Lines of Code (excl. blank lines): 0

## 2020-12-14, Monday, Day D: Codebreakers

Ma'am, we intercepted another encrypted message:

```Python
cipher = [ 8, 12, 30, 11, 8,
13, 10, 4, 18, 19,
4, 13, 31, 30, 14,
1, 4, 17, 4, 13,
30, 18, 2, 7, 20,
7, 30, 0, 20, 5,
30, 3, 4, 13, 30,
18, 2, 7, 20, 7,
18, 2, 7, 17, 28,
13, 10, 4, 13, 30,
8, 12, 30, 10, 4,
11, 11, 4, 17 ]
```

Build a decryption machine that applies all instructions of the Enigma machine in reverse order.

Hints:
> Codify your algorithm from yesterday!

> If you're stuck, use the enigma machine as a starting point.
> One possible way to write the inverse mechanism looks very much
> like the original enigma machine with just minor changes.

> IF YOU'RE STUCK, THEN ASK YOUR CHIEF SCIENTIST NEXT DOOR!!!

Lines of Code (excl. blank lines): 9-10

## 2020-12-15, Tuesday, Day E: Multidimensional confusion

Gosh, darn it! The encryption machine has been enhanced from 1d to 2d:

```Python
cipher = [[0, 0], [6, 2], [1, 2], [10, 0],
[1, 0], [1, 1], [4, 0], [10, 0],
[4, 0], [0, 0], [2, 2], [2, 1],
[1, 1], [5, 2], [8, 1], [10, 0],
[2, 2], [4, 0], [10, 0], [1, 0],
[0, 0], [0, 2], [2, 1], [2, 0],
[1, 1], [6, 0], [0, 2], [2, 1],
[4, 2], [6, 0], [6, 0]]
```

Fortunately, our mole among has not been revealed yet and
managed to leak the blueprint of the second enigma revision as well:

```Python
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# TOP SECRET

import sys

cleartext = 'classified information example'.lower()

abc_2d = [# 0 1 2 j/i
['a', 'b', 'c'], # 0
['d', 'e', 'f'], # 1
['g', 'h', 'i'], # 2
['j', 'k', 'l'], # 3
['m', 'n', 'o'], # 4
['p', 'q', 'r'], # 5
['s', 't', 'u'], # 6
['v', 'w', 'x'], # 7
['y', 'z', 'ö'], # 8
['ü', 'ä', 'ß'], # 9
[' ', ',', '-']] # 10

def find_index(c, array2d):
height = len(array2d)
for i in range(height):
row = array2d[i]
width = len(row)
for j in range(width):
if array2d[i][j] == c:
return list([i, j])
return None

cipher = []
for c in cleartext:
idx = find_index(c, abc_2d)
cipher.append(idx)

print(cipher)
```

Hints:
> Zero-based numbering, i.e. initial element of a sequence is assigned the index 0, rather than the index 1!

> IF YOU'RE STUCK, THEN ASK YOUR CHIEF SCIENTIST NEXT DOOR!!!

Lines of Code (excl. blank lines): 0

## 2020-12-16, Wednesday, Day F: The lull before the storm

After four exhausting days abroad, helping out the federal intelligence service, you are glad to be back at your office.
Sitting in front of your desk, you are looking forward to some relaxing time for the rest of the week,
without further adventures or surprises ☀️⛱️😎🌅

*\*Ping\** You got mail! 📨

A mail without any hint about the sender. Just a plain mail with a link to an
[Excel sheet](https://berrendorf.inf.h-brs.de/~jmeng2m/ccc2020/day16/secret.xlsx).
What could that be?

Of course you cannot simply click on this link, too dangerous.
Use Python library [`Pandas`](https://www.journaldev.com/33306/pandas-read_excel-reading-excel-file-in-python) to
read and print this [Excel sheet `secret.xlsx`](https://berrendorf.inf.h-brs.de/~jmeng2m/ccc2020/day16/secret.xlsx).

Hints:
> [`Pandas` has support for various URL shemes built-in, e.g. `http`](
https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.read_excel.html).
> It is not necessary to download the Excel sheet with `urllib` or `requests` libraries.

> [To read Excel sheets with Pandas, install and use `openpyxl`](https://stackoverflow.com/a/65266270/6490710):
> In Anaconda run `%pip install openpyxl`, then pass `engine='openpyxl'` to `read_excel`.

> Optionally, pass `header=None` as an extra argument to `read_excel`,
> so `Pandas` won't use the first row for the column labels.

Lines of Code (excl. blank lines): ~3-5

## 2020-12-17, Thursday, Day XVI: Pandas do lay eggs

Still halfdozing, with freshly brewed tea ☕ in your left hand and stirring in your breakfast 🍯 with the other,
you are sitting in front of your computer 💻 and sift halfhearted through your mails 📥📬.
Suddenly, a mail 📧 grabs your attention. It is empty except for a link to another
[Excel sheet](https://berrendorf.inf.h-brs.de/~jmeng2m/ccc2020/day17/secret.xlsx).
What is that? 🔐

Hints:
> You may download the spreadsheet with any browser.

> You may inspect the spreadsheet with e.g. Microsoft Excel.

> Pass `header=None` as an extra argument to
> [`read_excel`](https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.read_excel.html),
> so `Pandas` won't use the first row for the column labels.

Lines of Code (excl. blank lines): ~8-10

## 2020-12-18, Friday, Day XVII: Pythonic arms race

Finally, friday is here!
Before enjoying your well-deserved vacation, you have a couple of hours left to ramp up your programming skills 🔧⚙️
Two days before you had to extract data from a single cell.
Yesterday the location string was split across a table row.
The next logical step is a two-dimensional array aka a full table with rows and columns 📈 📊

Download this [spreadsheet](https://berrendorf.inf.h-brs.de/~jmeng2m/ccc2020/day18/secret.xlsx) using any browser
and open it in e.g. Microsoft Excel to inspect its contents. Use Python to concatenate all cell values into a single
one-dimensional array of characters aka a string and `base64`-decode it!

Hints:
> [`pandas.DataFrame.shape`](https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.shape.html)
> will return the dimensionality of the DataFrame.

> [`pandas.DataFrame.at`](https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.at.html) and/or
> [`pandas.DataFrame.iat`](https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.iat.html)
> access a single value for a row/column label pair (`at`) or a row/column pair by integer position (`iat`).

> Many roads lead to rome.
> You could use loop(s) with [`at`](https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.at.html)
> /[`iat`](https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.iat.html) to iterate over
> the DataFrame's 2d array. Or you could use a more functional style of programming using
> [`to_numpy`](https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.to_numpy.html),
> [`flatten`](https://numpy.org/doc/stable/reference/generated/numpy.ndarray.flatten.html) and
> [`join`](https://stackoverflow.com/a/4481731/6490710). Or you could come up with a completely different approach.

Lines of Code (excl. blank lines): ~5-13

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