Author Topic: Sudoku (Read 13282 times)

ElyDave · « **Reply #25 on:** 29 February, 2016, 06:29:48 am »

anyone else come across a non-unique solution?

I had one with 4 spaces left, two pairs of numbers say 3s and 4s which I could put in two combinations without affecting the validity of the answer.

Never seen that again.

arabella · « **Reply #26 on:** 01 March, 2016, 06:44:22 pm »

yes, but I couldn't say when. a set of pairs that could go either way around.
usually if I have one I then resort to arithmetic and find there is in fact only one solution - but arithmetic ony an option if you are doing killer sudoku, which is why i prefer it to the normal kind - the normal sudoku you could substitite shapes for numbers and it'll still work.
(circle, oval, triangle, square, oblong, lozenge, star, pentagon, hexagon, for example)

Riggers · « **Reply #27 on:** 03 March, 2016, 01:23:43 pm »

I can't quite believe what I'm reading.

Wowbagger · « **Reply #28 on:** 01 May, 2016, 08:31:01 pm »

Tricky one today.

http://www.killersudokuonline.com/play.html?puzzle=D2kkas63774&year=2016

It seemed to be very easy initially, and I completed about half the puzzle in no time, but I really struggled with the second half.

Wowbagger · « **Reply #29 on:** 02 June, 2020, 03:16:15 pm »

Since the lockdown began, I have resumed solving the daily Killer Sudoku.

The website I frequent issues a number of puzzles each day. Their Monday puzzle is reckoned to be the easiest, and they gradually increase in difficulty through the week, Sunday's being the hardest. I don't normally have much trouble, although some of the tougher ones can have me racking my brains.

Today's was labelled "Easy" but I thought it was a right git.

https://www.killersudokuonline.com/play.html?puzzle=D2kmxyp5267&year=2020

Some chap called Andrew Stuart has written a rather good Sudoku Solver which I occasionally use to give me some hints. It's not that uncommon, with the harder puzzles, for his solver to run out of techniques before I do.

https://www.sudokuwiki.org/killersudoku.htm

SoreTween · « **Reply #30 on:** 05 June, 2020, 09:30:53 pm »

I'm badly out of practice but sodding hell! I must be over an hour in and I've not found my first solid number yet. The Outrageous linked in reply #8 was a doddle compared to this Easy.

(don't like the 'check' feature on that site, it's too easy to accidentally cheat)

mattc · « **Reply #31 on:** 05 June, 2020, 09:59:51 pm »

Quote from: Wowbagger on 02 June, 2020, 03:16:15 pm

Since the lockdown began, I have resumed solving the daily Killer Sudoku.

The website I frequent issues a number of puzzles each day. Their Monday puzzle is reckoned to be the easiest, and they gradually increase in difficulty through the week, Sunday's being the hardest. I don't normally have much trouble, although some of the tougher ones can have me racking my brains.

Today's was labelled "Easy" but I thought it was a right git.

https://www.killersudokuonline.com/play.html?puzzle=D2kmxyp5267&year=2020

Nope, beats me! (I can do all the Times ones with a biro, any grade, although the hardest sometimes take me quite a long time to get going. I always have to scribble some notes somewhere. If I printed this out I could persevere for a bit longer, but I can't promise I'd get started. I don't really enjoy spending 30 minutes getting started; it's the Middle Game that's usually most fun.)

I would not call it "Easy".

SoreTween · « **Reply #32 on:** 10 June, 2020, 09:35:00 am »

Woot! Got there eventually. Lack of practice wasn't a factor, that's a harder puzzle than I've ever persisted with before. I did use the solver for two hints, both things I should have spotted (7 in row A early on, can't recall the other).

Stepping right through with the solver afterwards I find three things:
1) It makes a lot of use of innies & outies. I must learn to spot those, I didn't know that trick.
2) The solver only used rules down to Killer combos (hard). I used those as my primary weapon.
3) That means I'm not even at the stage of using all the 'tough' strategies so I have a great deal left to learn/figure out.

Yesterday' 'easy', is.

Wowbagger · « **Reply #33 on:** 10 June, 2020, 11:00:39 pm »

The annoying thing about "innies & outies" is that you sometimes have to revisit them multiple times, each time narrowing down the possible range of numbers until you have eliminated all but the right answer(s). When you have to add up 4 rows or columns to find the difference between what is stated in the cages and 225, it is areal test for your mental arithmetic. But I reckon that these are a good way to keep the brain active and (hopefully) keep the dementia fairy at bay.

It's got to the point that I can solve most puzzles in well under an hour now.

SoreTween · « **Reply #34 on:** 13 June, 2020, 11:15:30 am »

Have you looked at this week's Mind Bender? I'm stuck so I put it into the solver. I'm quite pleased that it too is stuck having made just one more elimination than me.

I can't see a cell that is key enough to be worth going down the guess route.

Set this cookie to go straight to that point:

(click to show/hide)

Wowbagger · « **Reply #35 on:** 13 June, 2020, 11:30:02 am »

I did that a couple of days ago but my machine seems to have forgotten it.

I'll have another go. I did today's https://www.killersudokuonline.com/play.html?puzzle=D368c7k5278&year=2020 in about 45 minutes.

PS I don't know how to set a cookie...

Wowbagger · « **Reply #36 on:** 13 June, 2020, 01:25:41 pm »

Progress...

Wowbagger · « **Reply #37 on:** 13 June, 2020, 01:28:36 pm »

Wowbagger · « **Reply #38 on:** 13 June, 2020, 02:18:46 pm »

I got there in the end.

I think the trickiest bit initially was realising the limited number of possibilities in the top row, once you've got the 789 triple for the 24-cage starting on A1. All the rest must be one of 123456 and the cage of 6 cells totalling 39 must be made of 456789. That then limits the two squares A6 & A7 to 4, 5 and 6.

Later on there was the elimination of 7 from A1 and J1. That was dependent on realising that C1 is valued at 6. 6 aded to the 18 in the cage starting at E1 meant that neither of those squares could be 7.

SoreTween · « **Reply #39 on:** 15 June, 2020, 08:59:47 pm »

Quote from: Wowbagger on 13 June, 2020, 02:18:46 pm

I got there in the end.

I'm no further forward.

Quote from: Wowbagger on 13 June, 2020, 02:18:46 pm

I think the trickiest bit initially was realising the limited number of possibilities in the top row, once you've got the 789 triple for the 24-cage starting on A1. All the rest must be one of 123456 and the cage of 6 cells totalling 39 must be made of 456789. That then limits the two squares A6 & A7 to 4, 5 and 6.

Got all that very quickly. Getting from there to the reductions in your first screenshot has be stumped. Still working through the available combinations.

Wowbagger · « **Reply #40 on:** 16 June, 2020, 10:29:07 am »

Can you post a screenshot of where you are up to? I can't recall my thought processes.

I've reopened the puzzle and loaded it as far as the "Sudoku Solver" takes you before it runs out of ideas.

SoreTween · « **Reply #41 on:** 16 June, 2020, 01:02:26 pm »

One step forward, 5&6 placed in B4, B5 & A7.

I've not fully investigated the implications of that step yet. Not having much time at the moment but that seems to help. I keep seeing things in the first couple of minutes I'd not spotted in earlier long sessions (I have 3 on the go at the moment)

[ETA]Ah yes, the 4 within the 39 group has been pushed inside square 2, that's the next step. Investigating....

Wowbagger · « **Reply #42 on:** 16 June, 2020, 01:44:36 pm »

(click to show/hide)

SoreTween · « **Reply #43 on:** 16 June, 2020, 03:46:35 pm »

(click to show/hide)

Wowbagger · « **Reply #44 on:** 16 June, 2020, 04:00:18 pm »

You can also make progress with the innies/outies in Column 7.

That, in turn, has implications for the 3 cells total value 15 in the bottom RH block , and of course the bottom row of the RH middle block..

Wowbagger · « **Reply #45 on:** 18 July, 2020, 11:08:17 pm »

https://www.killersudokuonline.com/play.html?puzzle=D37shr35313&year=2020

That was an utter sod.

Normally, even for supposedly "hard" puzzles, a point comes when it just falls into place. That didn't for me. I was battering it for a couple of hours, I reckon.

Pickled Onion · « **Reply #46 on:** 19 July, 2020, 01:47:28 pm »

Yesterday's Guardian killer (https://www.theguardian.com/lifeandstyle/2020/jul/18/killer-sudoku-719) has overlapping inner shapes. Is that a thing, or a mistake? I failed at the point where I got to filling in that area, and can't be arsed to backtrack as I can't see that I went wrong anywhere.

Wowbagger · « **Reply #47 on:** 19 July, 2020, 02:26:29 pm »

A quick count-up gave a grand total of 405 (9*45), so I think that must have been a mistake. Otherwise, that extra square would have been counted twice and the total would have ben >405.

Wowbagger · « **Reply #48 on:** 18 December, 2020, 03:22:04 pm »

https://www.killersudokuonline.com/play.html?puzzle=D3sk7v25465&year=2020

Moderate, allegedly. Took me ages. Very hard to unpick, right to the end.

JennyB · « **Reply #49 on:** 28 December, 2020, 05:45:18 pm »

I'm addicted to Simon Anthony's solves on Cracking the Cryptic; elegant handcrafted Sudoku variants and other puzzles solved in real time with a running commentary of his reasoning.

Here's one that I'm particularly proud of having worked out for myself - eventually: The Miracle Sudoku