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Go Counting
Go Counting

Go Counting

Hard

Instructions

Count the scored points on a Go board.

In the game of go (also known as baduk, igo, cờ vây and wéiqí) points are gained by completely encircling empty intersections with your stones. The encircled intersections of a player are known as its territory.

Write a function that determines the territory of each player. You may assume that any stones that have been stranded in enemy territory have already been taken off the board.

Write a function that determines the territory which includes a specified coordinate.

Multiple empty intersections may be encircled at once and for encircling only horizontal and vertical neighbours count. In the following diagram the stones which matter are marked "O" and the stones that don't are marked "I" (ignored). Empty spaces represent empty intersections.

+----+
|IOOI|
|O  O|
|O OI|
|IOI |
+----+

To be more precise an empty intersection is part of a player's territory if all of its neighbours are either stones of that player or empty intersections that are part of that player's territory.

For more information see wikipedia or Sensei's Library.

To complete this exercise, you need to implement the following functions:

  • territories returns the coordinates (1 based, top left is (1,1)) of the points in each territory along with who "owns" the territory.

  • territoriesFor returns the territory that contains the coordinate along with the owner of the territory. If the coordinate does not point to an empty location, returns Nothing.

A territory is owned by one of the players if that player's stones are the only stones adjacent to the territory.

You will find the type signatures already in place, but it is up to you to define the functions.

Last updated 23 November 2022
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