# 15-puzzle Solvability

Simple

15-puzzle is a quite old and famous puzzle, which had its own peak of interest!

In this mission you are given a position of tiles - a list of 4 lists of equal length with all integers from 1 to 16 incl. in arbitrary order (but number 16 always stands for empty place!). Your function should return a boolean value, if this combination of tiles is solvable (may be transformed by valid moves to "normal" order) or not, as True or False respectively.

Here is an interesting video about the puzzle itself and its solvability problem with the algorithm of checking explained. So if you don't like spoilers, you may try to solve the mission first without watching the video.

Input: A position of tiles as a list of 4 lists of integers from 1 to 16 incl.

Output: Solvability of puzzle as boolean value.

Examples:

```assert (
fifteen_puzzle([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]])
== True
)
assert (
fifteen_puzzle([[15, 14, 13, 12], [11, 10, 9, 8], [7, 6, 5, 4], [3, 2, 1, 16]])
== False
)
assert (
fifteen_puzzle([[1, 5, 9, 13], [2, 6, 10, 14], [3, 7, 11, 15], [4, 8, 12, 16]])
== True
)
assert (
fifteen_puzzle([[1, 3, 2, 4], [5, 7, 6, 8], [9, 11, 10, 12], [13, 15, 14, 16]])
== True
)
```

How itâ€™s used: it's always interesting, what inner logic stands behind well-known games and puzzles.

Preconditions:

• len(position) == len(position[i]) == 4;
• set(sum(position, [])) == {1, 2, ... 16}.

Settings
Code:
Other:
Invalid hot key. Each hot key should be unique and valid
Hot keys:
•  to Run Code: to Check Solution: to Stop:
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`

`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.

Pair Programming (Beta-version)

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