The New Sudoku Players' Forum

by **urhegyi** » Fri Jun 19, 2020 10:39 am

: help.png (15.05 KiB) Viewed 1000 times

Can someone on this forum find help me to find another way of solving this sudoku which is less difficult. Perhaps I didn't saw a logical step and made it to complicated?
I can solve it, so you can ignore the basics. I am interested in different ways to solve it. Other people may have idea's which are not simular to mine.

by **SpAce** » Fri Jun 19, 2020 12:45 pm

Hi urhegyi,

urhegyi wrote:
help.png
Can someone on this forum find help me to find another way of solving this sudoku which is less difficult. Perhaps I didn't saw a logical step and made it to complicated?

It's not a trivial puzzle, as it probably requires several steps even from a decent player. Not very difficult ones, though. (Disclaimer: I don't have time to solve it manually, so I just used Hodoku to analyze it a bit). Hodoku claims it can solve it in a single step but it requires such a horrible net that I'm not willing to verify it (Hodoku's net solutions aren't always reliable, so I have my doubts). In any case, Hodoku's default path (with my settings) takes 12 steps (of which some are most likely unnecessary, but I haven't checked which ones):

2-String Kite: -1 r4c2
2-String Kite: -8 r3c2
AIC[5]: -2 r1c7,r78c9 -> basics, 3 singles
AIC[5]: -5 r1c2
AIC[4]: -6 r3c6
AIC[4]: -1 r6c7
AIC[4]: -8 r6c2
ALS-AIC[5]: -6 r2c6 (*) -> pointing pair
XY-Chain[8]: -8 r5c6,r6c3 -> 5 singles
W-Wing: -6 r4c2
W-Wing: -6 r6c4 -> 10 singles, pointing pair
XY-Wing: -9 r2c2,r9c3; stte

All but one of those steps are short and basic AICs. Only step 8 is a bit complicated because it uses two relatively big ALSs. Still, it's a normal AIC too. (Btw, you have to turn on "Preferences::Steps::Allow ALS in chains" for Hodoku to find it. For some weird reason it's not on by default.)

So, no need for kraken fishes or other complicated techniques. (I haven't seen that a kraken fish is ever needed anyway, and very few human players would use them at all. Normal krakens (which Hodoku calls "Forcing Chain Verity") that use cells, rows, columns, or boxes, are usually simpler and in my experience almost always find the same eliminations.)

(*) Here's the most complicated step 8:

Code: Select all: .-------------------.--------------------.-------------. | 1 f79 f579 | 4 59 a[6]8 | b68 3 2 | | 3 f89(6) f89(6) | 29 1 28-6 | 7 4 5 | | 2 456 4568 | 7 3568 38 | c168 9 16 | :-------------------+--------------------+-------------: | 4 356 e156 | e29 e69 e126 | d135 7 8 | | 9 58 2 | 13 7 48 | 45 6 13 | | 7 136 168 | 136 48 5 | 34 2 9 | :-------------------+--------------------+-------------: | 6 2 17 | 5 34 134 | 9 8 47 | | 8 17 3 | 16 46 9 | 2 5 47 | | 5 49 49 | 8 2 7 | 36 1 36 | '-------------------'--------------------'-------------'

(6=8)r1c6 - r1c7 = (8-1)r3c7 = r4c7 - (1=269'5)r4c6543 - (5=798'6)b1p2356 => -6 r2c6

Or with the last node broken into two pieces:

(6=8)r1c6 - r1c7 = (8-1)r3c7 = r4c7 - (1=2695)r4c6543 - (5=79)r1c23 - (9=86)r2c23 => -6 r2c6

--

I also tried to find a shorter path with krakens (but not nets). A pretty reasonable one takes five steps with 3 simple AICs (one ALS) and 2 relatively simple krakens (cell and row):

1) ALS XY-Wing: (6=8)r1c6 - (8=4)r5c6 - (4=136)r539c9 => -6 r1c9 (-> 3 singles)
2) Kraken Cell (168)r6c3 => -4 r6c5 (-> 2 singles)

Code: Select all: (1)r6c3 - (1=7)r7c3 - (7=4)r7c9 || (6)r6c3 - r6c4 = r8c4 - (6=4)r8c5 || (8)r6c3 - (8=4)r6c5 => -4 r6c5

3) AIC[5]: (5=8)r5c2 - (8=4)r5c6 - (4=1)r7c6 - (1=7)r7c3 - r1c3 = (7)r1c2 => -5 r1c2
4) Kraken Row (5r3) => -9 r1c2 (-> 13 singles)

Code: Select all: (5)r3c2 - (5=8)r5c2 - (8=4)r5c6 - (4=1)r7c6 - (1=7)r7c3 - r1c3 = (7)r1c2 || (5-4)r3c3 = r3c2 - (4=9)r9c2 || (5)r3c5 - (5=9)r1c5 => -9 r1c2

5) XY-Chain[4]: (6=9)r2c2 - (9=5)r1c3 - (5=1)r4c3 - (1=6)r6c3 => -6 r23c3,r6c2; stte

--

Does that give you new ideas at all?

by **urhegyi** » Fri Jun 19, 2020 5:59 pm

: kraken.png (21.98 KiB) Viewed 963 times

Thank you Space for your tips. Through your explication I saw the kraken fish can be replaced through a normal kraken. What I did were your step 3 and 4 as my first 2 steps. The third was my kraken fish I replaced through this:

by **SpAce** » Fri Jun 19, 2020 11:58 pm

urhegyi wrote:Thank you SpAce for your tips. Through your explication I saw the kraken fish can be replaced through a normal kraken. What I did were your step 3 and 4 as my first 2 steps. The third was my kraken fish I replaced through this:

No problem. Glad that my tips helped! In fact, your new solution is better than my proposal, as it solves it in the same 5 steps with just one kraken. It can also be easily upgraded to a simple double-kraken to shave off one step. That in turn can be written easily as a nested AIC, if one wishes. Here's my updated path with that and three simple AICs of lengths [3..4] (no ALS or groups needed):

AIC[4]: (2=4)r8c7 - r6c7 = (4-8)r6c5 = r3c5 - r3c7 = (8)r1c7 => -2 r1c7 (*)
AIC[9] (nested): (5)r13c2 = [(8)r5c2 = r5c6 - r6c5 = (85-4)r3c53 = (4971)r3918c2 - r7c3 = (14-8)r75c6 = (8)r5c2] => -5 r5c2 (**)
AIC[3] (M2-Wing): (1=6)r6c3 - r6c4 = (6-1)r8c4 = (1)r8c2 => -1 r46c2,r7c3
AIC[3] (H-Wing): (5=9)r1c3 - (9=4)r9c3 - r9c2 = (4)r3c2 => -5 r3c2 (*); stte

(*) Alternate ALS moves for the first and the last step: Show

(**) Step 2: uncompressed; as a double-kraken; as a matrix; as two steps: Show

PS. Next time it would be nice if you posted the puzzle string like this, so it doesn't have to be manually entered into a solver:

Code: Select all: 1..4.....3...1.7.5.......9.4.......89.2.7..6......5.296......8.8.3..9.......27...

(You can get it from Hodoku::Edit::Copy Givens.)

Website · by **denis_berthier** » Sat Jun 20, 2020 7:52 am

urhegyi wrote:
help.png
Can someone on this forum find help me to find another way of solving this sudoku which is less difficult. Perhaps I didn't saw a logical step and made it to complicated?
I can solve it, so you can ignore the basics. I am interested in different ways to solve it. Other people may have idea's which are not simular to mine.

A solution with no chain with length longer than 5:

Hidden Text: Show

The New Sudoku Players' Forum

solution needs a lot of AIC's and even a kraken fish

solution needs a lot of AIC's and even a kraken fish

Re: solution needs a lot of AIC's and even a kraken fish

Re: solution needs a lot of AIC's and even a kraken fish

Re: solution needs a lot of AIC's and even a kraken fish

Re: solution needs a lot of AIC's and even a kraken fish