I couldn't solve Brainbashers July the 8th 'very hard' sudoku without resorting to 'super hard'
techniques, and that, 3 or 4 times.
I suppose I overlooked something, but can anybody remember it being especially hard, or even harder
than usual
I couldn't solve Brainbashers July the 8th 'very hard' sudoku without resorting to 'super hard'
techniques, and that, 3 or 4 times.
I suppose I overlooked something, but can anybody remember it being especially hard, or even harder
than usual
On 17/07/2022 10:13, gerson wrote:
"Mike Terry" wrote in message news:PYGdnes3fZABp03_nZ2dnUU7-aPNnZ2d@brightview.co.uk...
On 14/07/2022 02:51, gerson wrote:
I couldn't solve Brainbashers July the 8th 'very hard' sudoku without resorting to 'super hard'
techniques, and that, 3 or 4 times.
I suppose I overlooked something, but can anybody remember it being especially hard, or even
harder than usual
I just had a go at it. I was using the auto-pencil marks and highlighting features and it took me
7 minutes. So for me that elevates it out of the "came out easily" category (under 3 minutes),
but it didn't seem especially hard. Normally I have to follow "hooks(?)" around the grid to
gradually eliminate numbers, which I'm guessing is an advanced technique, but I didn't need that
at all for this puzzle. (But I'm not really clear on what constitutes a super-hard technique.)
Most days I just do the "very hard" puzzle, because it takes me about the amount of time I have to
spend on it (5-10 mins), and if it takes <3 mins I'm dissatisfied so I do the super-hard one.
Mike.
Thanks
By 'super hard techniques' I was referring to the last four things on the list you get when you
click on his 'Sudoku help page' in the Notes. Anyhow, I'd like to know what "hooks(?)" "round the
grid' is. Is it what I call chaining, such as,
- if this one's a 3 then that one's an 8 which makes that other one a 2 and so on - ?
I don't instantly recognise my "hooks" in the list of techniques on the help page. It's rather like
the "remote pairs", except it's much more general than that. ("remote pairs" can be considered a
simple case of my technique.) If you take the remote pairs examples and just focus on ONE of the
pairs of digits, that's more like it.
Basically, the approach is to highlight occurences of a chosen digit, and identify two of them such
that one or other of those two must be correct. Then any common buddies of the two cannot be that
digit. In practice we start with one of the digits, and say "if this square ISN'T the chosen digit,
then [any valid deductions working around the grid until we identify some other square that MUST be
the chosen digit]". Then we eliminate common buddies. (So there is a strong element of focussed
"chaining" in your sense, but there is a specific goal we are working towards - not just random "I
wonder what happens if this square is a 6".
Anyway, looking at the list of techniques, a number of them are just special cases of my technique.
E.g. X-Wing, Remote Pairs, XY-Wing, XYZ-Wing are all variations of my technique, and I'd spot all of
them in a Brainbashers sudoku through that mechanism if not more directly. (X-Wing is just a
cut-down Swordfish, which in turn is a cut-down generalised pattern applying to any number of
columns, not just 2 or 3! I look for the general pattern which covers X-Wing, but I've never
thought to learn "XYZ-Wing" as a pattern as I'd (probably) find it with the hook(?) pattern anyway,
so it wouldn't be any extra help...)
Hmmm, I searched for "hook" and sudoku etc. and found a link which does explain the technique I mean
but only in a simplified form.
<https://www.sudokudragon.com/guidehook.htm>
[click the "stop" button on the page to turn off the annoying auto-play, then use left and right
buttons to step through the demo]
My explanation (referring to the linked web page diagrams) would be:
- We are focussing on 6's (On BrainBashers I would highlight all 6's)
- [step through demo to step 6 of 22]
- the highlighted square Dc is our starting point
- Dc can be 6, but IF IT'S NOT, then...
- it's the 8, so Ac is 7, and Ca is 6. Bingo! [###]
- Put another way - EITHER Dc or Ca is 6. (This is the important point.)
- So any common buddies of those two squares can't be 6
In the given scenario, that means Da and Ea can't be 6.
The demo says "we must have 3 squares..." but that's not really required at all - what we must have
is the starting square Dc which may be the 6, and the [###] chain of deductions above (any length)
leading to another square also having to 6 (if the starting square is assumed not to be 6). Then we
can apply the common buddy conclusion for those two cells. So it's all quite flexible, but also
needs some experience/practice to work out /fruitful/ applications of the rule!
I used the rule a couple of times in todays "very hard" puzzle, so if you like I could try to
reproduce the positions where I used it to explain further. (But being able to highlight the chosen
number occurences is quite important in practice as it helps direct our goal, hence which deduction
links might be more fruitful. Highlighting will be missing in any diagram I manage to post!)
Regards,
Mike.
"Mike Terry" wrote in message news:PYGdnes3fZABp03_nZ2dnUU7-aPNnZ2d@brightview.co.uk...
On 14/07/2022 02:51, gerson wrote:
I couldn't solve Brainbashers July the 8th 'very hard' sudoku without resorting to 'super hard'
techniques, and that, 3 or 4 times.
I suppose I overlooked something, but can anybody remember it being especially hard, or even
harder than usual
I just had a go at it. I was using the auto-pencil marks and highlighting features and it took me 7
minutes. So for me that elevates it out of the "came out easily" category (under 3 minutes), but it
didn't seem especially hard. Normally I have to follow "hooks(?)" around the grid to gradually
eliminate numbers, which I'm guessing is an advanced technique, but I didn't need that at all for
this puzzle. (But I'm not really clear on what constitutes a super-hard technique.)
Most days I just do the "very hard" puzzle, because it takes me about the amount of time I have to
spend on it (5-10 mins), and if it takes <3 mins I'm dissatisfied so I do the super-hard one.
Mike.
Thanks
By 'super hard techniques' I was referring to the last four things on the list you get when you
click on his 'Sudoku help page' in the Notes. Anyhow, I'd like to know what "hooks(?)" "round the
grid' is. Is it what I call chaining, such as,
- if this one's a 3 then that one's an 8 which makes that other one a 2 and so on - ?
On 14/07/2022 2:51 am, gerson wrote:
I couldn't solve Brainbashers July the 8th 'very hard' sudoku without resorting to 'super hard'
techniques, and that, 3 or 4 times.
I suppose I overlooked something, but can anybody remember it being especially hard, or even
harder than usual
Damn you, I've now tried it six times. No joy.
I couldn't solve Brainbashers July the 8th 'very hard' sudoku
without resorting to 'super hard' techniques, and that, 3 or 4
times.
I suppose I overlooked something, but can anybody remember it
being especially hard, or even harder than usual
On 17/07/2022 17:16, Richard Heathfield wrote:
On 14/07/2022 2:51 am, gerson wrote:
I couldn't solve Brainbashers July the 8th 'very hard' sudoku
without resorting to 'super hard' techniques, and that, 3 or 4
times.
I suppose I overlooked something, but can anybody remember it
being especially hard, or even harder than usual
Damn you, I've now tried it six times. No joy.
The BrainBashers sudokus are machine-generated somehow, and I
can't imagine that the generation processes doesn't perform a
solve-check using just the allowed solution techniques, which
will all be programmed into the generator as runtime selectable
options.
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