The New Sudoku Players' Forum

by **Guest** » Thu Jun 02, 2005 5:56 am

On many hard, or very hard puzzles, there is often a point in the game where logic no longer comes into play. Then trial and error must be used - i.e guessing on of two numbers and continuing the puzzle to see whether it fails somewhere down the line or not. Surely claims that all Sudoku puzzles can be solved by logic alone are false? Any comments?

by **Animator** » Thu Jun 02, 2005 10:47 am

I've solved many hard and very hard puzzles and never came to such a point...

It seems to me that you are missing some techniques... Perhaps it would be a good idea to post a puzzle on which you are stuck?

by **Guest** » Tue Jun 07, 2005 2:08 pm

Can anyone give me a hand with this puzzle? I've come to the trial and error stage. Logic doesn't seem to work for me....

Code: Select all: 9-- 7-8 -45 47- -95 --- 85- -42 -7- 649 581 723 237 964 158 --- 273 496 7-- 856 -34 --- --9 -67 3-- --7 ---

cheers

by **Animator** » Tue Jun 07, 2005 2:25 pm

Take a close look at the number 1.

If you look carefully then you know where it has to go in column 1.

(Also, can you do me a favor? Next time you post a grid, then please include the category...)

by **Vereth** » Tue Jul 01, 2008 11:47 am

Which logic must be used for this one?

000700800000040030000009001600500000010030040005001007500200600030080090007000002

or as a grid:

Code: Select all: --- 7-- 8-- --- -4- -3- --- --9 --1 6-- 5-- --- -1- -3- -4- --5 --1 --7 5-- 2-- 6-- -3- -8- -9- --7 --- --2

It is proved to have an unique solution, but it seems it can be calculated only with brute force.

by **Glyn** » Tue Jul 01, 2008 2:33 pm

Vereth The puzzle you have given is extremely hard. It may be a transformation of an already known puzzle in the hardest puzzles thread, I'm sure someone can easily verify that. It requires nested forcing moves.

by **Pat** » Tue Jul 01, 2008 3:03 pm

Vereth wrote:Which logic must be used for this one?

Code: Select all
. . . 7 . . 8 . . . . . . 4 . . 3 . . . . . . 9 . . 1 6 . . 5 . . . . . . 1 . . 3 . . 4 . . . 5 . . 1 . . 7 5 . . 2 . . 6 . . . 3 . . 8 . . 9 . . . 7 . . . . . 2

SuDoku Explainer 1.2.1 rates it 10.6

by **Glyn** » Tue Jul 01, 2008 4:19 pm

Pat It's what I would call a 'breeze' for Sudoku Explainer (where the breeze refers to the processor fan).

by **daj95376** » Tue Jul 01, 2008 4:20 pm

Code: Select all: ...7..8......4..3......9..16..5......1..3..4...5..1..75..2..6...3..8..9...7.....2 c258 Swordfish (finned) <> 7 [r3c1] -or- r258 Swordfish (finned) <> 7 [r3c1] 5r3c7 5r5c9 4r8c9 4r3c7 <> 5 [r3c7] (chain) +--------------------------------------------------------------------------------+ | 12349 24569 123469 | 7 1256 2356 | 8 256 4569 | | 12789 256789 12689 | 168 4 2568 | 2579 3 569 | | 2348 245678 23468 | 368 256 9 | 247 2567 1 | |--------------------------+--------------------------+--------------------------| | 6 24789 23489 | 5 279 2478 | 1239 128 389 | | 2789 1 289 | 689 3 2678 | 259 4 5689 | | 23489 2489 5 | 4689 269 1 | 239 268 7 | |--------------------------+--------------------------+--------------------------| | 5 489 1489 | 2 179 347 | 6 178 348 | | 124 3 1246 | 146 8 4567 | 1457 9 45 | | 1489 4689 7 | 13469 1569 3456 | 1345 158 2 | +--------------------------------------------------------------------------------+

At this point, just test the five different possibilities for '7'. It may be Brute Force, but is nested forcing chains/nets really any better?

Code: Select all: ...7..8......4.73..7...9..16..57....71..3..4...5..1..75..2..67..3..87.9...7.....2 ...7..8...7..4..3......9.716..5.7...71..3..4...5..1..75..27.6...3..8.79...7.....2 ...7..8...7..4..3......9.716..57....71..3..4...5..1..75..2.76...3..8.79...7.....2 ...7..8...7..4..3......97.16..57....71..3..4...5..1..75..2..67..3..87.9...7.....2 *** ...7..8..7...4..3......9.7167.5......1..37.4...5..1..75..27.6...3..8.79...7.....2

by **champagne** » Tue Jul 01, 2008 4:26 pm

Vereth wrote:Which logic must be used for this one?

000700800000040030000009001600500000010030040005001007500200600030080090007000002

It can be solved with nets of AICs crossing AHS or ALS, but it is a long long way.

by **ronk** » Tue Jul 01, 2008 5:20 pm

Glyn wrote:Vereth The puzzle you have given is extremely hard. It may be a transformation of an already known puzzle in the hardest puzzles thread, I'm sure someone can easily verify that. It requires nested forcing moves.

It has popped up before here.

by **Vereth** » Tue Jul 01, 2008 8:16 pm

Great work! Thanks to all!

daj95376 wrote:
Code: Select all
...7..8......4..3......9..16..5......1..3..4...5..1..75..2..6...3..8..9...7.....2 c258 Swordfish (finned) <> 7 [r3c1] -or- r258 Swordfish (finned) <> 7 [r3c1] 5r3c7 5r5c9 4r8c9 4r3c7 <> 5 [r3c7] (chain) +--------------------------------------------------------------------------------+ | 12349 24569 123469 | 7 1256 2356 | 8 256 4569 | | 12789 256789 12689 | 168 4 2568 | 2579 3 569 | | 2348 245678 23468 | 368 256 9 | 247 2567 1 | |--------------------------+--------------------------+--------------------------| | 6 24789 23489 | 5 279 2478 | 1239 128 389 | | 2789 1 289 | 689 3 2678 | 259 4 5689 | | 23489 2489 5 | 4689 269 1 | 239 268 7 | |--------------------------+--------------------------+--------------------------| | 5 489 1489 | 2 179 347 | 6 178 348 | | 124 3 1246 | 146 8 4567 | 1457 9 45 | | 1489 4689 7 | 13469 1569 3456 | 1345 158 2 | +--------------------------------------------------------------------------------+

At this point, just test the five different possibilities for '7'. It may be Brute Force, but is nested forcing chains/nets really any better?

Code: Select all
...7..8......4.73..7...9..16..57....71..3..4...5..1..75..2..67..3..87.9...7.....2 ...7..8...7..4..3......9.716..5.7...71..3..4...5..1..75..27.6...3..8.79...7.....2 ...7..8...7..4..3......9.716..57....71..3..4...5..1..75..2.76...3..8.79...7.....2 ...7..8...7..4..3......97.16..57....71..3..4...5..1..75..2..67..3..87.9...7.....2 *** ...7..8..7...4..3......9.7167.5......1..37.4...5..1..75..27.6...3..8.79...7.....2

Maybe testing the 7's could be simplified by using the Pattern Overlay Method?

by **hobiwan** » Tue Jul 01, 2008 8:54 pm

This doesn't really belong here but since we were just discussing Sue de Coq elsewhere here are two Sue de Coqs in my solver's solution:

AAALS, B tripply linked, C with additional candidate:

Code: Select all: .---------------------.----------------------.---------------------. | 1349 B25 134-69| 7 A1256 A236 | 8 B256 4-69 | | 189 257 689 | C18 4 2568 | 279 3 569 | | 348 257 3468 | C38 256 9 | 247 2567 1 | :---------------------+----------------------+---------------------: | 6 489 3489 | 5 7 248 | 1239 128 389 | | 7 1 2 | 9 3 68 | 5 4 68 | | 3489 489 5 | 48 26 1 | 239 268 7 | :---------------------+----------------------+---------------------: | 5 489 1489 | 2 19 347 | 6 178 348 | | 2 3 14 | 6 8 457 | 147 9 45 | | 1489 6 7 | 134 159 345 | 134 158 2 | '---------------------'----------------------'---------------------' Sue de Coq: r1c56 - {12356} (r1c28 - {256}, r23c4 - {138}) => r1c39<>6

Additional candidate in C:

Code: Select all: .------------------.------------------.-------------------. | 1349 25 39 | 7 125 36 | 8 56 49 | | 189 27 689 | 18 4 56 | 27 3 59 | | 348 257 368 | 38 25 9 | 247 567 1 | :------------------+------------------+-------------------: | 6 49 349 | 5 7 2 | 39 1 8 | | 7 1 2 | 9 3 8 | 5 4 6 | | 389 89 5 | 4 6 1 | 39 2 7 | :------------------+------------------+-------------------: | 5 489 1489 | 2 19 47 | 6 C78 3 | | 2 3 B14 | 6 8 -457 | A147 9 A45 | | 89 6 7 | 13 59 34 | 14 C58 2 | '------------------'------------------'-------------------' Sue de Coq: r8c79 - {1457} (r8c3 - {14}, r79c8 - {578}) => r8c6<>4

by **cpu.write** » Sun Jul 06, 2008 7:34 pm

Anonymous wrote:Can anyone give me a hand with this puzzle? I've come to the trial and error stage. Logic doesn't seem to work for me....

Code: Select all
9-- 7-8 -45 47- -95 --- 85- -42 -7- 649 581 723 237 964 158 --- 273 496 7-- 856 -34 --- --9 -67 3-- --7 ---

cheers

I am not conversant with the terminology used for puzzles such as this; however, I have come up with some mathematical techniques that allow me to solve some of these puzzles. Therefor, I will explain the terminology that I use and go from there.

I number the boxes, with the upper left box being box #1 and the lower right box being box #81.

By writing down (or whatever) the numbers that are not automatically eliminated because they are already present in the same row, column or 3 X 3 that each respective open box is in, I generated the following Raw Possibility Matrix (God, I hope I got this right--there's probably a web site or a download or something that'll do this automatically--and if not I can write one--but I don't know where it is):

Code: Select all: ----------------------------------------------------------- | 9 | 126 | 1236 # 7 | 136 | 8 # 236 | 4 | 5 | ----------------------------------------------------------- | 4 | 7 | 1236 # 136 | 9 | 5 # 23368 | 138 | 129 | ----------------------------------------------------------- | 8 | 5 | 136 # 136 | 4 | 2 # 369 | 7 | 19 | =========================================================== | 6 | 4 | 9 # 5 | 8 | 1 # 7 | 2 | 3 | ----------------------------------------------------------- | 2 | 3 | 7 # 9 | 6 | 4 # 1 | 5 | 8 | ----------------------------------------------------------- | 15 | 18 | 158 # 2 | 7 | 3 # 4 | 9 | 6 | =========================================================== | 7 | 12 | 12 # 8 | 5 | 6 # 29 | 3 | 4 | ----------------------------------------------------------- | 15 | 128 | 12458 # 134 | 123 | 9 # 25 | 6 | 7 | ----------------------------------------------------------- | 3 | 1269 | 124568 # 14 | 12 | 7 # 2589 | 18 | 129 | -----------------------------------------------------------

Please check boxes 56 and 57. These can only hold the values of 1 or 2. Since this is the case, no other boxes in that 3 X 3 or row can hold either of those values.

Code: Select all: ----------------------------------------------------------- | 9 | 126 | 1236 # 7 | 136 | 8 # 236 | 4 | 5 | ----------------------------------------------------------- | 4 | 7 | 1236 # 136 | 9 | 5 # 23368 | 138 | 129 | ----------------------------------------------------------- | 8 | 5 | 136 # 136 | 4 | 2 # 369 | 7 | 19 | =========================================================== | 6 | 4 | 9 # 5 | 8 | 1 # 7 | 2 | 3 | ----------------------------------------------------------- | 2 | 3 | 7 # 9 | 6 | 4 # 1 | 5 | 8 | ----------------------------------------------------------- | 15 | 18 | 158 # 2 | 7 | 3 # 4 | 9 | 6 | =========================================================== | 7 | 12 | 12 # 8 | 5 | 6 # 9 | 3 | 4 | ----------------------------------------------------------- | 15 | 8 | 458 # 134 | 123 | 9 # 25 | 6 | 7 | ----------------------------------------------------------- | 3 | 69 | 4568 # 14 | 12 | 7 # 2589 | 18 | 129 | -----------------------------------------------------------

Using this information, one can easily establish that box 65 must contain the number 8 (its raw possibilities are only 1, 2 or 8).

This removes the possibility of any other box in that row, column or 3 X 3 containing the number 8.

Code: Select all: ----------------------------------------------------------- | 9 | 126 | 1236 # 7 | 136 | 8 # 236 | 4 | 5 | ----------------------------------------------------------- | 4 | 7 | 1236 # 136 | 9 | 5 # 23368 | 138 | 129 | ----------------------------------------------------------- | 8 | 5 | 136 # 136 | 4 | 2 # 369 | 7 | 19 | =========================================================== | 6 | 4 | 9 # 5 | 8 | 1 # 7 | 2 | 3 | ----------------------------------------------------------- | 2 | 3 | 7 # 9 | 6 | 4 # 1 | 5 | 8 | ----------------------------------------------------------- | 15 | 1 | 158 # 2 | 7 | 3 # 4 | 9 | 6 | =========================================================== | 7 | 12 | 12 # 8 | 5 | 6 # 9 | 3 | 4 | ----------------------------------------------------------- | 15 | 8 | 45 # 134 | 123 | 9 # 25 | 6 | 7 | ----------------------------------------------------------- | 3 | 69 | 456 # 14 | 12 | 7 # 2589 | 18 | 129 | -----------------------------------------------------------

Because of this, box number 47 must contain the number 1 (it is in the same column as box 65, and its raw possibilities are 1 and 8).

This removes the number 1 from the possibilities in the row, column and 3 X 3 in which box 47 is found.

Code: Select all: ----------------------------------------------------------- | 9 | 26 | 1236 # 7 | 136 | 8 # 236 | 4 | 5 | ----------------------------------------------------------- | 4 | 7 | 1236 # 136 | 9 | 5 # 23368 | 138 | 129 | ----------------------------------------------------------- | 8 | 5 | 136 # 136 | 4 | 2 # 369 | 7 | 19 | =========================================================== | 6 | 4 | 9 # 5 | 8 | 1 # 7 | 2 | 3 | ----------------------------------------------------------- | 2 | 3 | 7 # 9 | 6 | 4 # 1 | 5 | 8 | ----------------------------------------------------------- | 5 | 1 | 58 # 2 | 7 | 3 # 4 | 9 | 6 | =========================================================== | 7 | 2 | 12 # 8 | 5 | 6 # 9 | 3 | 4 | ----------------------------------------------------------- | 15 | 8 | 45 # 134 | 123 | 9 # 25 | 6 | 7 | ----------------------------------------------------------- | 3 | 69 | 456 # 14 | 12 | 7 # 2589 | 18 | 129 | -----------------------------------------------------------

Because of this, box 46 must contain the number 5--its raw possibilities are 1 and 5. Also because of this, box 56 must contain the number 2--it is in the same row as box 47.

Look at the lower left 3 X 3 carefully.

The 5 in box 46 removes that possibility from all other boxes in its column.

Code: Select all: ----------------------------------------------------------- | 9 | 26 | 1236 # 7 | 136 | 8 # 236 | 4 | 5 | ----------------------------------------------------------- | 4 | 7 | 1236 # 136 | 9 | 5 # 23368 | 138 | 129 | ----------------------------------------------------------- | 8 | 5 | 136 # 136 | 4 | 2 # 369 | 7 | 19 | =========================================================== | 6 | 4 | 9 # 5 | 8 | 1 # 7 | 2 | 3 | ----------------------------------------------------------- | 2 | 3 | 7 # 9 | 6 | 4 # 1 | 5 | 8 | ----------------------------------------------------------- | 5 | 1 | 58 # 2 | 7 | 3 # 4 | 9 | 6 | =========================================================== | 7 | 2 | 12 # 8 | 5 | 6 # 9 | 3 | 4 | ----------------------------------------------------------- | 1 | 8 | 45 # 134 | 123 | 9 # 25 | 6 | 7 | ----------------------------------------------------------- | 3 | 69 | 456 # 14 | 12 | 7 # 2589 | 18 | 129 | -----------------------------------------------------------

Thus, box 64 must contain the number 1--it is in the same column as box 46, and its raw possibilities are 1 and 5.

Because box 56 contains the number 2, this removes the possibility that any other box in its row contains that number.

Code: Select all: ----------------------------------------------------------- | 9 | 26 | 1236 # 7 | 136 | 8 # 236 | 4 | 5 | ----------------------------------------------------------- | 4 | 7 | 1236 # 136 | 9 | 5 # 23368 | 138 | 129 | ----------------------------------------------------------- | 8 | 5 | 136 # 136 | 4 | 2 # 369 | 7 | 19 | =========================================================== | 6 | 4 | 9 # 5 | 8 | 1 # 7 | 2 | 3 | ----------------------------------------------------------- | 2 | 3 | 7 # 9 | 6 | 4 # 1 | 5 | 8 | ----------------------------------------------------------- | 5 | 1 | 58 # 2 | 7 | 3 # 4 | 9 | 6 | =========================================================== | 7 | 2 | *1* # 8 | 5 | 6 # 9 | 3 | 4 | ----------------------------------------------------------- | *1* | 8 | 45 # 134 | 123 | 9 # 25 | 6 | 7 | ----------------------------------------------------------- | 3 | 69 | 456 # 14 | 12 | 7 # 2589 | 18 | 129 | -----------------------------------------------------------

Therefor, box 57 must contain the number 1--it is in the same 3 X 3 as box 56, and its raw possibilities are 1 and 2.

But this is impossible. Box 57 cannot contain the number 1 because box 64, in the same 3 X 3, was already shown to contain the number 1.

Therefor, I conclude that there is an error in your existing solution to this puzzle. Please provide the raw puzzle.

by **Glyn** » Sun Jul 06, 2008 9:20 pm

cpu.write Unfortunately what you call the Raw Possibility Matrix is incorrect. Here is the actual scenario. You can try it again from here. It is very straightforward.

This puzzle was posted 3 years ago so it is really a dormant thread.

Code: Select all: .---------------------.---------------------.---------------------. | 9 126 1236 | 7 13 8 | 236 4 5 | | 4 7 1236 | 136 9 5 | 2368 18 12 | | 8 5 136 | 136 4 2 | 369 7 19 | :---------------------+---------------------+---------------------: | 6 4 9 | 5 8 1 | 7 2 3 | | 2 3 7 | 9 6 4 | 1 5 8 | | 15 18 158 | 2 7 3 | 4 9 6 | :---------------------+---------------------+---------------------: | 7 129 12 | 8 5 6 | 29 3 4 | | 15 128 12458 | 134 123 9 | 258 6 7 | | 3 12689 124568| 14 12 7 | 2589 18 129 | '---------------------'---------------------'---------------------'

The New Sudoku Players' Forum

This cannot be solved by logic

This cannot be solved by logic

10.6