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Dominosa is a logic puzzle with a similar feel to Sudoku, and I've recently added it to Donimoes, my collection of domino puzzles and games. Given a grid of numbers, you have to lay out the dominoes so they match the numbers, without duplicated or missing dominoes. See Monday's problem for complete rules and and an example solution.

Today's problem is a little bigger and a little more challenging. Good luck, and post your solution as an answer.

Challenge problem

If you like this puzzle, watch for a more challenging problem on Friday.

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  • $\begingroup$ Looking forward to Fridays! :) $\endgroup$
    – Beastly Gerbil
    Apr 29, 2020 at 14:39

2 Answers 2

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Final answer:

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Step by step:

1:

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0-1 and 2-2 only appear here, and this creates a trapped domino bottom right.

2:

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1-1 and 1-2 now only appear here. This creates trapped dominoes top left

3:

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The 1 dominoes can now be completed.

4:

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From here we can fill in lots of trapped dominoes

5:

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More trapped dominoes gets us to here. There is already a 0-0 so the only configuration is the final answer.

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Final solution:

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Explanation (dark blue):

  • There's only one place for the 0-1 and the 2-2

  • This forces the lower right corner to be the 3-3

  • Now there is only one place for the 1-1

Light blue:

  • Not sure if this is the most efficient, but the 3-3 already having a place means that the triplet of 3s in the right two columns needs to be 3-1, 3-2, 3-5, either using the 1 in the rightmost column or the 1 in the second column from the right. If the former, the 4-4 is in the top right, which means the two fours in the leftmost column need to be covered by a 4-2 (second row) and 4-1 (third row), leaving a 1-5 in the first row and in the fifth row, which leads to a contradiction. So the 3-1 and 3-5 are in the second column from the right, and the 3-2 in the rightmost one.

  • This forces the positions of the 4-5 (fifth row), 0-3 (bottom row), 1-4 (rightmost column), 3-4 (first row), 0-5 (second row), 0-0 (first row)

  • The 0-0 already being positioned means the lower left corner must be the 0-4 and 0-2.

  • This forces the 2-5 in the third column, 2-4 in the fourth and 5-5 in the third.

Finally (green):

  • The only place for the 4-4 is the first column

  • This forces the 1-2 and 1-5.

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  • $\begingroup$ Weird, why was this downvoted? $\endgroup$
    – oAlt
    Apr 29, 2020 at 15:09
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    $\begingroup$ Lack of freehand circles? $\endgroup$
    – Glorfindel
    Apr 29, 2020 at 15:11
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    $\begingroup$ Although you beat Beastly Gerbil's solution by a minute, I accepted theirs because I think it's more elegant without backtracking. However, you still have my upvote and my effusive thanks for solving my puzzle. It gladdens my heart when people play with my games and puzzles! $\endgroup$
    – Don Kirkby
    Apr 29, 2020 at 15:42

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