Count Inversions Count Inversions
Elementary+
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In computer science and discrete mathematics, an inversion is a pair of places in a sequence where the elements in these places are out of their natural order. So, if we use ascending order for a group of numbers, then an inversion is when larger numbers appear before lower number in a sequence.

Check out this example sequence: (1, 2, 5, 3, 4, 7, 6) and we can see here three inversions
- 5 and 3;
- 5 and 4;
- 7 and 6.

You are given a sequence of unique numbers and you should count the number of inversions in this sequence.

Input: A sequence as a tuple of integers.

Output: The inversion number as an integer.

Example:

count_inversion((1, 2, 5, 3, 4, 7, 6)) == 3
count_inversion((0, 1, 2, 3)) == 0

How it is used: In this mission you will get to experience the wonder of nested loops, that is of course, if you don't use advanced algorithms.

Precondition: 2 < len(sequence) < 200
len(sequence) == len(set(sequence))
all(-100 < x < 100 for x in sequence)

Settings
Code:
CheckiO Extensions

CheckiO Extensions allow you to use local files to solve missions. More info in a blog post.

In order to install CheckiO client you'll need installed Python (version at least 3.8)

Install CheckiO Client first:

pip3 install checkio_client

Configure your tool

checkio --domain=py config --key=

Sync solutions into your local folder

checkio sync

(in beta testing) Launch local server so your browser can use it and sync solution between local file end extension on the fly. (doesn't work for safari)

checkio serv -d

Alternatevly, you can install Chrome extension or FF addon

checkio install-plugin
checkio install-plugin --ff
checkio install-plugin --chromium

Read more here about other functionality that the checkio client provides. Feel free to submit an issue in case of any difficulties.

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