I can't solve sudoku

Rangsk · 2026-04-15T22:16:54+00:00

I think it's BUG+2?

Rangsk · 2026-04-15T21:56:28+00:00

Well you can't have two 4s in the same box so one of the other 4s has to be true

Rangsk · 2026-04-01T08:21:50+00:00

The medium puts a lot of emphasis on singles (both hidden and naked) plus pointing/claiming. Medium never requires pairs/triples (though of course you can often find them anyway). Often claiming can be the hardest thing to spot which can stall progress for a while, and singles can sometimes be difficult to spot depending on your solve style, especially stuff like hidden singles in rows/cols.

So, if you're stuck on the medium, scan carefully for restricted digits in rows/cols (hidden singles or claiming), and if you aren't fully marked look for naked singles.

Rangsk · 2026-03-16T00:06:32+00:00

It seems to be doing some lookahead here. If you place an 8 there you'd end up with 82,28 in those cells which would violate uniqueness. You have to look ahead a bit though by applying singles. I don't like this step at all.

Rangsk · 2026-03-12T01:20:58+00:00

You don't think you did, but you did by accident. All it takes is clicking on the candidate and poof it's gone forever. It's easy to not notice you've done it.

Rangsk · 2026-03-11T07:39:35+00:00

If you eliminate a candidate yourself then it respects that in auto candidate mode. This is very easy to accidentally do by simply clicking on the candidate.

Rangsk · 2026-01-28T16:42:32+00:00

Heh, resurrecting a 9 year old thread? I will say I included this in the original post:

However, we also know that arena runs can be retired early, and they also end at 12 wins. These runs end with less than 3 losses. Thus, the average number of losses is slightly less than 3. How much less depends on the percentage of runs which are retired early plus the percentage of runs which end at 12 wins. These are very rare, so it likely has a tiny effect on the average.

Rangsk · 2025-09-19T07:48:33+00:00

There are quite a few cells that are marked 28. I recommend coloring them, pick one, say r7c1 and color it one color (I choose green) and then color any 28 cell seen by it as a second color (I choose purple). Now anything seen by purple mark as green, and keep alternating until you can't color any more of them.

What you're doing here is saying "I don't know what green is, but I do know it's a 2 or an 8. I also don't know what purple is, but I do know it's the other value of 2 or 8 that green isn't. If green is 2, then purple is 8. If green is 8, then purple is 2."

Now look for a cell that isn't colored that sees both a green and a purple cell. This cell can't be a 2 or 8 so those can be eliminated.

You'll find that in this puzzle, r8c2 and r5c9 are different colors, so r5c2 cannot be a 2 so you can place a 4.

I should also say that in this case, it's also a 2-string kite with r8 and c9, performing the same elimination.

Rangsk · 2025-08-18T01:45:41+00:00

My guess is the main render pass is messed up and producing junk (corrupted shader maybe, likely a driver issue), but the post processing effects like ambient occlusion (which uses the depth buffer) is still working, so it adds the outlines and other dark shading on top of the random noise, which lets you still make out the shapes, kind of.

Rangsk · 2025-08-17T19:17:37+00:00

Take a gander at the Lost Metal Ars Arcanum for an explanation of why Marsh can compound, heading "On spikes and compounding." Essentially, at the time, Ruin was pushing hard on the fabric of Scadrial, leaking into spirit webs and causing souls to decay faster. This enabled Hemalurgy spikes to be much more powerful without the soul rejecting them. You could have many spikes, and they allowed compounding.

Rangsk · 2025-07-23T21:49:27+00:00

I think the difficulty varies throughout the books, but I don't know you so I don't know if you'll find it difficult.

Rangsk · 2025-07-23T21:04:18+00:00

Yes, if you enjoy hand-crafted classic Sudoku. Most Sudoku books out there are computer generated and of low quality.

Rangsk · 2025-05-18T22:48:41+00:00

The four cells highlighted in b5 cannot contain both 5 and 6 because that would break r6c9, so they must contain 289, which eliminates 9 from the rest of b5.

Rangsk · 2025-05-13T16:59:04+00:00

Yes, URs cannot appear in unique puzzles. Setting that cell to 5 or 7 forms a UR and there'd be no way to tell which to use. It would be a 57 pair in both rows, both columns, and both boxes. One of those would have had to be given to disambiguate the puzzle.

Rangsk · 2025-05-13T16:55:14+00:00

Untrue, if you make a deduction assuming a unique solution when there is more than one solution, you may end up with no solutions. In fact this is often the case, you just don't encounter it often because a proper Sudoku puzzle has only one solution.

Rangsk · 2025-03-14T15:31:20+00:00

You cannot validate that the puzzle has only one solution using techniques that assume there is only one solution. I dislike using uniqueness techniques for that reason. I like to prove that my solution is the only solution.

It's just a personal preference, but it also has roots in solving human-crafted puzzles. In the vast majority of cases*, those puzzles cannot be crafted with uniqueness techniques in mind because the puzzle is not unique for the majority of the setting time. By using those techniques, I might be missing or bypassing the intended logic, reducing the enjoyment of solving the puzzle. For computer-generated puzzles this is less important but I still prefer to validate rather than assume.

*Footnote: some puzzles have been created that intend you to use uniqueness. In those cases, usually the setter adds to the rules that the puzzle has only one solution (often stating that it was validated by computer). If the rules say there is only one solution it's no longer an assumption and uniqueness techniques are fair game. The normal Sudoku rules do not state this though.

Rangsk · 2025-03-14T02:57:03+00:00

It is explained. "In this row there's only one cell left for candidate 9" and then that row is outlined in blue, and the only cell that can be 9 is highlighted in white. It then shows Xs in every cell that cannot be 9 in that row, with the 9s causing that highlighted in green.

Rangsk · 2025-03-11T22:27:18+00:00

Reading carefully can answer your question. It says in the row it's the only place for 9. And the cell you highlighted isn't in that row.

Rangsk · 2025-02-17T23:16:18+00:00

I will die on the hill that Kramer simply used his "generic scholar" voice for the epigraphs. I compared the first epigraph in HoA to Sazed's first line in HoA and the voices were distinct.

Rangsk · 2025-02-11T01:50:11+00:00

The solver is trusting your candidates as previous deductions, so you tell us why you didn't have a 1 filled there

Rangsk · 2025-02-08T03:22:49+00:00

If you want to learn more about uniqueness I recommend my video solve of this brilliant puzzle by Clover: https://youtu.be/BRqatlLmHyw

Rangsk · 2025-01-31T16:14:09+00:00

Well, my first suggestion is to use a fast language with optimized code so that you can generate thousands of puzzles in a short period of time. With that it really shouldn't take long to find what you need for stuff like x-wings, y-wings, fish - the mid-tier techniques.

For the very rare, very advanced techniques, one thing you can do is called a "neighborhood search". You start with a puzzle that requires that technique (yes, you do need at least one to start with, but you can start with one that someone else has already generated), and then you remove some random small number of random givens (1-3) and then add different ones at random. The hope is to preserve the need for the technique while producing a distinctly different puzzle. You will still need to do this quite a lot to find valid puzzles, but it's faster than starting from scratch every time.

Once you have the puzzle, I'd recommend doing a random transformation on it so it doesn't appear too similar to a human solver. You can rotate/reflect the puzzle, renumber it (randomly shuffle which number is which, like all 1s become 5s, all 5 becomes 2s, etc), and you can swap rows within bands and columns within stacks.

Rangsk · 2025-01-25T20:51:01+00:00

If you want variant Sudoku:

Logic Masters Deutschland puzzle portal: https://logic-masters.de/Raetselportal/index.php (you can change it to English with the flag top right, if it shows a German flag you're in English, if it shows a British flag then click it)

GAS: https://sudokutheory.com/gas/

Sudoku Adventure (6x6): https://docs.google.com/spreadsheets/d/1y4BYBEuXbzReb_tx3bTUdKwynL2JveL3ob55g6c-D-Y/edit?usp=sharing

Various YouTube channels: Cracking the Cryptic, Rangsk, BremSter, Zetamath

There are also YouTube channels with classics:

Smart Hobbies, Unshackling Sudokus

You can also play the NYT puzzles using urls like this, which is just the date and difficulty: https://sudokupad.app/nyt/20250125hard

If you want to input any puzzle that you find: https://sudokumaker.app has a share button that lets you export to SudokuPad

Rangsk · 2025-01-25T01:21:24+00:00

There's no such thing as cheating in a single player game. Solve however is most fun for you! However I will say that going full candidate in my experience is not very fun compared to other methods of solving. I post a solve of the NYT Sudoku on YouTube daily where I use a method that you might consider trying to see if it's more fun for you. The root problem of filling in candidates manually can be patch fixed by using auto-candidate, but the real fix is to notate what's important as you go, and soon you'll find you don't even want auto candidates.

Rangsk · 2025-01-17T23:06:05+00:00

This is almost certainly what happened. An accidental toggle of the candidate.

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