Fortress Sudoku

by Clover

• Play it ↗
• Difficulty: medium

For vacation puzzle 2 I have another Generally Approachable Sudoku (GAS) from Cracking the Cryptic. The mechanic this time around feels a little less fantastical than some of the thermo or arrow puzzles, but I liked it just the same because it doesn't involve any math. My journey to solution required a restart because I soft-locked myself with an incorrect deduction somewhere in my original solve, but that restart actually made me appreciate the puzzle on a whole new level.

I found the first two fortress deductions easily enough, slotting a 5 and 9 in squares 2 and 8, where a single grey cell is surrounded by 4 orthogonals and the corners are already filled. Easy peasy. The later deductions took a bit more thinking, but also made me feel awful clever when I noticed them.

Here are some of ones I uncovered:

• A grey cell can never be a 1.

• 9s can never border a grey cell at the orthogonal. They're either in the grey cell or somewhere that's not orthogonal.

• A grey cell must be at minimum 1 + the number of orthogonal cells.

The coolest moment in this puzzle was actually restarting it because I made a mistake. Sure, I was frustrated. But when I started working through the grid again from scratch, I noticed that all of my newfound deduction powers meant solving the puzzle in a completely different way. On my second playthrough, I finished out the middle row in almost 5 minutes, where previously I was futzing around with no real direction. Now that's a great feeling.

In my second playthrough, I ended up filling the grey cells relatively quickly. I started to get pretty good at applying the deductions; "this square must be at minimum one of these values. By sudoku, these higher values can't be in the grey. That means they also can't be orthogonal to the grey, since the grey would have to be larger. Aha!" Most of my time was actually spent doing normal sudoku.

I've noticed with these GAS puzzles that when I'm blocked during normal sudoku I need to pay more attention to the rows and columns. When I stop tunnel-visioning on the boxes, I often notice that there are only two or three possible digits in a row/column, and that's all I need to slot the proper digit. I don't think I'm very good at regular sudoku.

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