Smythe Dakota wrote:I prefer to get there via http://www.sudoku.org.uk/kakuroflash/kakuro.html

Thanks for this direct link, I didn't know it.

Smythe Dakota wrote:I suppose those stand for Gentle, Medium, Tough, and Difficult, or something like that.

If they use the same notation as for Sudoku and Jigsaw, M is Moderate and D Diabolical.

I don't like much the white arrows in the black cells. When I try to copy the puzzle, it's confusing. And it's ugly (well, personal tastes ...). Also I don't like having access only to the last 10; if I want 10 more, I have to wait 10 days (that'll be next season!).

Yesterday evening, I've tried the 10 I could see there (2 Gs, 3 Ms, 4 Ts, 1 D). I don't see much difference in difficulty: they are all in W2 except 3 Ts (sic, not Ds) in W3. In Kakuro, W2 implies that any elimination can be done by considering only one sector at a time (see my previous examples of whips[2]).

Even for the 3 in W3, each has at most 2 or 3 whips[3], and there's only one case in total of such a whip that involves several sectors.

So, as Bill suggested, they are quite easy, compared to the atk ones (even restricted to the Medium ones) - recalling however that I had only a small sample.

One other limitation is size: they are all 10x10 (at least the 10 I could see). This puts drastic restrictions on the possible combinations and there are many small sized sectors.

On atksolutions.com (I have no shares there), they have puzzles with 5 different sizes (10 to 14) and with 3 levels of difficulty. I like their clean and sober presentation with blue cells and white numbers inside. Unfortunately, you can choose the level but not the size and the 10x10 ones do not come out often.

Notice that size is not the only factor of difficulty: even with size 10, difficulty can be much higher than on the Mepham website.

I've seen a 10x10 atk one in W11 (in the Wn rating, difficulty increases ~exponentially wrt n). In the 14x14 collection, I've even seen one in W22.

This is consistent with what I had noticed for Sudoku long ago: all the Mepham puzzles are relatively easy.

However, the case of Kakuro puzzles can hardly be compared with Sudoku: for lack of any discussion forum, we have little knowledge of how people solve them and of what should be considered as difficult for manual solving. Scanning the Kakuro part of this forum, I've seen two that seemed to be harder than usual:

- the Surfertje thread ("Tough ending"), but it's "only" in W6;

- the h3lix thread ("Incredibly difficult kakuro (14x14)"), but it's "only" in W7.

There also seems to be two different approaches: people looking for puzzles amenable to treatment by surface sums (and thus doing much arithmetic) and people preferring to track allowed combinations (and hopefully to do little arithmetic). My approach is clearly of the second kind, pushed to the extreme of doing no arithmetic at all - although, of course, I can also occasionally use surface sums. It seems Bill prefers the first type of puzzles.

Smythe Dakota wrote:I once saw a puzzle that appeared to have been created by chopping off the bottom two rows or so from a larger puzzle. (That made the diagram lose the 180-degree rotational symmetry common in newspaper puzzles.) As a result, there was at least one vertical "word" consisting of just one digit. But the puzzle still specified the "sum", i.e. the digit, in that cell.

Formally, this doesn't raise any problem; allowing one-cell sectors can make it easier to create hard puzzles. But I agree it isn't not very elegant.