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Smallest Groups with Two Eyes

September 3, 2011 Leave a comment

Today’s riddle is for the Go player. Your task is to find all the smallest groups with two eyes and place them all together (with the corresponding enclosing enemy stones) in a single 19 \times 19 board. Let me give you some tips first:

  • Smallest groups in the corner: In the corner, six stones are the minimum needed to complete any group with two eyes. There are only four possibilities, and I took the liberty of placing them on the board for you:

    goboard

  • Smallest groups on the side: Consider any of the smallest groups with two eyes on a side of the board. How many stones do they have? [Hint: they all have the same number of stones] How many different groups are there?
  • Smallest groups in the interior: Consider finally any of the smallest groups with two eyes in the interior of the board. How many stones do they have? [again, they all have the same number of stones]. How many different groups are there?

Since it is actually possible to place all those groups in the same board, this will help you figure out how many of each kind there are. Also, once finished, assume the board was obtained after a proper finished game (with no captures): What is the score?

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