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This puzzle is part of the Puzzling Stack Exchange Advent Calendar 2022. The accepted answer to this question will be awarded a bounty worth 50 reputation.

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Today's door leads to a signature "easy" puzzle by Anonymus25! I know, some of my recent puzzles haven't performed well (and by recent, I mean many months ago), but I'm back and ready to try again! As I said before, this puzzle is "easy", but only if you truly understand this genre's deductions. It's a Circles and Squares!

Rules: Shade some cells such that all shaded cells form one single orthogonally connected area, and no 2x2 anywhere in the grid may be fully shaded (as in Nurikabe). All unshaded areas must form squares. Black circles are shaded, white circles are unshaded.

Some good example puzzles include this one by Athin and this one by me.

Here's a Penpa link to solve online.

P.S. The green, red, and brown are purely for aesthetics.

Christmas and Squares

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  • $\begingroup$ Nice puzzle! Loved the thought process gone into the puzzle, was a nice solve. $\endgroup$
    – Stevo
    Dec 6, 2022 at 7:14
  • $\begingroup$ What do red and green mean? $\endgroup$
    – msh210
    Dec 6, 2022 at 9:03
  • $\begingroup$ Purely for aesthetics, I'll add that (The red dots are Christmas ornaments, the green is the tree with a brown stalk) $\endgroup$ Dec 6, 2022 at 10:30

1 Answer 1

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Before we continue any further,

Green: Unshaded on this move
Blue: Shaded on this move
Grey: Shaded
Orange: Unshaded

Firstly, the most basic deductions: enter image description here

Then, we know these squares must be the case: enter image description here This is because the bottom middle square must be the same (3 by 3), while the left bottom corner square is quickly resolved. That resolves the squares around it as well. At the top, more shaded squares are resolved due to the white squares stopping bigger squares from emerging.

Because of the 2 x 2 square rule, these squares are made: enter image description here

Further deductions are then made: enter image description here

Simple small deductions are made here, still relatively easy: enter image description here

But stupid me, I made a mistake in the bottom left corner. Fixing it now: enter image description here The bottom right is also solved, as a 3 by 3 square cannot be made.

Then, most of the top right is solved: enter image description here

Finally, we get the middle resolved: enter image description here This is because Both white circles there, none of them could have been a 2 x 2 square without causing contradiction to the black squares.

Using the 2 x 2 shaded square rule on R4 C4: enter image description here , we get a lot of deductions

Almost sense the end... enter image description here , all those white circles all must be 1 x 1's.

enter image description here The white circle must be a 2 x 2 square due to the 2 x 2 shading rule...

enter image description here DONE! VOILA!

Finshed

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  • $\begingroup$ Correct! Thanks for the compliment, it really is a fun genre :D $\endgroup$ Dec 6, 2022 at 7:47

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