shithub: puzzles

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Slant uses the same generation strategy as Solo, despite not having
the property which devel.but claimed to be the reason why that
strategy works. A bit of thought revealed what the _real_ reason is
why this strategy works in some puzzles and not others, so I've
rewritten the paragraph to be more accurate.

[originally from svn r6158]

--- a/devel.but

+++ b/devel.but

@@ -3293,19 +3293,22 @@

 the 56 squares in the default setting!), so this tweaking strategy

 would be rather less likely to work well.

-A more specialised strategy is that used in Solo. Solo has the

-unusual property that the clues (information provided at the

-beginning of the puzzle) and the solution (information the user is

-required to fill in) are inherently interchangeable; therefore a

-simple generation technique is to leave the decision of which

-numbers are clues until the last minute. Solo works by first

-generating a random \e{filled} grid, and then gradually removing

-numbers for as long as the solver reports that it's still soluble.

-Unlike the methods described above, this technique \e{cannot} fail

-\dash once you've got a filled grid, nothing can stop you from being

-able to convert it into a viable puzzle. However, it wouldn't even

-be meaningful to apply this technique to (say) Pattern, in which the

-clues and the solution occupy completely different spaces.

+A more specialised strategy is that used in Solo and Slant. These

+puzzles have the property that they derive their difficulty from not

+presenting all the available clues. (In Solo's case, if all the

+possible clues were provided then the puzzle would already be

+solved; in Slant it would still require user action to fill in the

+lines, but it would present no challenge at all). Therefore, a

+simple generation technique is to leave the decision of which clues

+to provide until the last minute. In other words, first generate a

+random \e{filled} grid with all possible clues present, and then

+gradually remove clues for as long as the solver reports that it's

+still soluble. Unlike the methods described above, this technique

+\e{cannot} fail \dash once you've got a filled grid, nothing can

+stop you from being able to convert it into a viable puzzle.

+However, it wouldn't even be meaningful to apply this technique to

+(say) Pattern, in which clues can never be left out, so the only way

+to affect the set of clues is by altering the solution.

 (Unfortunately, Solo is complicated by the need to provide puzzles

 at varying difficulty levels. It's easy enough to generate a puzzle