[okayestjoel]

I believe none of the other 9 million have a unique solution. My nonogram solver goes over every possible configuration for each row and column based on the clues, and either fills in squares that must be filled (all possibilities overlap) or marks squares that must be empty. So if the solver reaches a point where there is ambiguity about what the next move is, then it is deemed not solvable (without guessing). A good example is a 5x5 puzzle where each row and column clue is "1": there are many possible 5x5 pixel grids that share those set of clues. Let me know if I'm misunderstanding your question.

[gus_massa]

You can try to codify for example https://pixelogic.app/every-5x5-nonogram#10725003 as "11-31-1-12-0+11-3-1-11-11" (is there an standard in the community?) and add the 9 million "unsolvable" codified strings to a vector and sort the vector, and then look for not repeated consecutive. For example, your case "1-1-1-1-1+1-1-1-1-1" should appear exactly 120 consecutive times in the sorted 9 million vector. Is there one that is not repeated?

Feature request: It would be nice to have a jump to unsolved puzzle. In section 1 it's difficult to find an empty one. Also, there is something weird with scrolling.

[okayestjoel]

In my mind, a well-formed nonogram is one that requires no backtracking. It's an interesting question though. I'll write some code in the next few days to check to see if my set of "unsolvable" puzzles include those with unique solutions given the clues.

Yeah, a "jump to unsolved" seems like its going to be essential. I'll work on that. I haven't heard of the scrolling issue. What device/browser are you using?

[quuxplusone]

On Android Chrome, "flinging" the scroll really far really fast sometimes keeps scrolling long beyond when I would have expected it to stop. But the page is so gigantic that that might just be the expected behavior.

FYI, I've also noticed that on Android (but not on desktop Chrome) sometimes single-tapping to remove a black square will leave a stray X behind. I think this is not a logic bug but rather a mobile input-recognition problem — that on mobile a single-tap is sometimes being recognized as a single-tap followed by a double-tap. (Quickly double-tapping an empty cell usually marks it with an X; although quickly double-tapping a filled cell usually just clears it, no X. So the symptom here is "I meant to single-tap a filled cell, but the game acted as if I'd single-tapped and then double-tapped the same cell again.")

[gus_massa]

> Scrolling

Chrome on Windows 10, nothing fancy. I move pick the scroll bar on the right with the mouse and move slowly down, perhaps to the middle and try to find a empty range, and when I release mouse it goes back near the top. As a guess: Have you tire to scroll at the ame time that other player is solving puzles in the same section? Try section 1.

> requires no backtracking

I have more background in Math Olympiads and plain Math. You can do backtracking to find a unique solution if you write all the options and discard all-1 of them. It sounds fancier if you call it "Reductio ad absurdum" :) . It's an usual trick, and my recommendation is that if you are in the middle of a problem that ask to fill a board and you have two(or more) options, first copy the board as many times as necessary and intermediately fill the two(or more) possibilities, to avoid forgetting one of them.

For games like minesweeper, sudoku or nonogram, my personal criteria is that if I can run the backtracking in my head, it's "thinking", but if I have to draw the two(or more) boards it's "backtracking".

For me it's probably only two options in a square, no further branching and only two or three steps deep before the contradiction. (If your name is Magnus, everything is "thinking".)

(By the way: Nice game implementation!)

[jsmith45]

Yeah, while large portions of the online logic puzzle communities tend to agree that puzzles should not require backtracking (after all one can often trivialize the intended logical solve path like that), it has proven difficult to define what should count as backtracking vs a simple obvious contradiction that should count as a logical step.

Ability to visualize it in your head, without needing to copy the board, or make temporary marks is certainly not unreasonable for complicated puzzles. That is the same rule as Simon uses for logic puzzles (mostly variant sudoku) on the YouTube channel Cracking the Cryptic.

It isn't the most satisfying way to delineate the dividing line, since how much a person can track in their head can vary, but coming up with other rules can be absurdly tricky. Especially if one wants to make a set of rules applicable to multiple types of logic puzzles. After all simple two to three step contradictions may be unusually powerful for some types of logic puzzles, while they can be the basic deduction type for a different one.

[gus_massa]

*intermediately -> immediately

[ghusbands]

It's common to assume that your solver encodes all the techniques that a human might reasonably use (without backtracking) but it's rarely the case. Someone could look at the clues in two columns and two rows at the same time, for example, and work out whether they together constrain something. (It's easier to see cases in minesweeper where quite long-range deductions can be made, especially when you're down to the last few mines.)

Look elsewhere in the thread and you'll see that there are 333,064 uniquely-solution grids that you have excluded.

[purpleidea]

> there is ambiguity about what the next move is

It's common to have situations where you need to guess between two possibilities, and then you'll find out that one is wrong and you need to backtrack.

So I hope the algo you implement only excludes puzzles with more than one solution. As long as there is exactly one solution, it's completely logical and fair game.

[MrJohz]

This is a philosophical point about what's considered solveable. For example, in the sudoku community, there's this idea of bifurcation, which is when you get to a point in a puzzle where there are two options to take, and you step through each option manually until you figure out which one is correct, and backtrack if necessary.

You can do an entire puzzle this way (just keep on trying options and seeing if they work), but this is generally not on. If you build a puzzle that can only be solved this way, then you've built a bad puzzle, at least by the standards of the sudoku solving community. On the other hand, most complex or variant sudoku puzzles will have moments where there are two or three possibilities for a cell, and you need to look at the immediate effects of those possibilities to figure out which one is correct. So clearly some amount of bifurcation and backtracking is fine.

Fwiw, in the nonograms I've done in various apps, there's almost never a need to guess between different possibilities. I don't know if that's because the puzzle format itself is fairly constrained, or if the apps typically try to exclude these cases. But typically, it's always possible to see a next step, without needing to try things out and guess.

[dietr1ch]

I really don't like the wording about multiple solutions not being logical. I get that instances where resolution doesn't lead you to the unique solution are annoying and don't scratch the right part of your brain, but I feel this audience could be more precise.

Here's a simple Nonogram to annoy everyone

# 1 1

1 . .

1 . .