Landing Site Landing Site
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That's one small step for [a] man, one giant leap for mankind.

Neil Alden Armstrong (1930-2012)

In this mission the size of the hexagonal grid is 12x9 ('A1' to 'L9').

  • It’s characteristics:
    • it’s flat-topped;
    • the alphabet letters represent columns and numbers represent rows;
    • the even columns are being pushed down.

You are given a set of obstacle hexes on the Moon as an input value. You have to return a set of all the candidate landing sites.

  • The conditions for the landing site hex:
    • the hex isn't an obstacle hex;
    • there’re no obstacle hexes in equidistant ( 1 or more ) hexes;
    • the above radius is the longest.
  • The outside of the hexagonal grid is always considered as an obstacle hex.
  • If there aren’t any landing sites, return an empty set.


assert landing_site({'E5', 'E7', 'F4', 'F6', 'G4', 'G6', 'H3', 'H5'}) == {'C3', 'J7'}
assert landing_site({'A4', 'C2', 'C6', 'C9', 'D4', 'D7', 'F1', 'F5',
                     'F8', 'G4', 'H7', 'I2', 'I5', 'I9', 'K3', 'K8', 'L5'}) == {'B7', 'E3', 'J6'}

Input: The obstacles on the Moon (a set of strings).

Output: A set of all the candidate landing sites (a set of strings).


  • all(re.fullmatch('[A-L][1-9]', i) for i in input)

How it is used: For finding the needed area.

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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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