Sudoku Players' Forum (clone)

i've been to over 20 websites daily to check out their puzzles and even bought many sudoku books... i want one that can actually stump me... if you find a hard puzzle on the internet can you please post up the link?

Try the "hardest" puzzles using pictures, letters, greek alphabet, etc instead of numbers.

Have you tried the Evil puzzles here?

http://www.websudoku.com/?level=4

D.

Try this one, which many solvers are stumped on:

| . . . | . 7 . | 9 4 . |
| . 7 . | . 9 . | . . 5 |
| 3 . . | . . 5 | . 7 . |
+-------+-------+----
| . 8 7 | 4 . . | 1 . . |
| 4 6 3 | . . . | . . . |
| . . . | . . 7 | . 8 . |
+-------+-------+---
| 8 . . | 7 . . | . . . |
| 7 . . | . . . | . 2 8 |
| . 5 . | 2 6 8 | . . . |

G

If you send me a fax on 02075026339 giving your fax number I can send you as many hard puzzles as you like.
You are right. I have also bought the Times, Guardian books etc. There is only a handful of really hard puzzles between them!
I have a computer program which checks them.
There are 3 types of hard puzzle.
They are all where the box converges on the row or columns.
There is a possibilty where only one number or even 2 numbers.
There is also another possibility. If you fax me I shall send you more details.
What ever you may read about on this forum, I can assure you Sudoku puzzles are very easy to compile and grade.
Most books are written by authors who have a only a very superficial knowledge of the subject and I don't just mean Carol Vorderman.
The last two puzzles in her book are the only real hard ones.
They use one of the 3 hard rules.

george-no1 wrote:Try this one, which many solvers are stumped on:

| . . . | . 7 . | 9 4 . |
| . 7 . | . 9 . | . . 5 |
| 3 . . | . . 5 | . 7 . |
+-------+-------+----
| . 8 7 | 4 . . | 1 . . |
| 4 6 3 | . . . | . . . |
| . . . | . . 7 | . 8 . |
+-------+-------+---
| 8 . . | 7 . . | . . . |
| 7 . . | . . . | . 2 8 |
| . 5 . | 2 6 8 | . . . |

G

I entered that one into Papocom sudoku and it said it was invalid

josper wrote:They are all where the box converges on the row or columns.
There is a possibilty where only one number or even 2 numbers.

Could you make yourself a little clearer please? - this has the potential to be a very interesting thread.

stuartn

http://www.brightonandhove.org/Sudolinks.htm

123HI wrote:i've been to over 20 websites daily to check out their puzzles and even bought many sudoku books... i want one that can actually stump me... if you find a hard puzzle on the internet can you please post up the link?

You won't find stumpers in books. Most of the Sudoku world follows the lead of Nikoli and Pappocom and creates puzzles aimed at people who will be solving them with a pen and paper using few if any pencil marks. If you solve in this fashion, the Very Hards created by Pappocom's software available on the website hosting this forum are challenging for most people. They're generally harder than those published in newspapers and books which usually top out at what would be Pappocom HARD.

However, if, like many of us, you want puzzles that might actually beat you, read this thread to start: http://forum.enjoysudoku.com/viewtopic.php?p=5666

Zeezop wrote:Try the "hardest" puzzles using pictures, letters, greek alphabet, etc instead of numbers.

Why not suggest turning the radio on very loud, dimming the lights very low and holding the pen with your foot? That'll make it difficult, though it doesn't answer the question.

Dinarius wrote:Have you tried the Evil puzzles here?

http://www.websudoku.com/?level=4

D.

I have. They are not difficult. Just tested 5 "evils" at random. SadMan rates them as "mild" or "medium". This compares with about "Medium" on Pappocom.

josper wrote:If you send me a fax on 02075026339 giving your fax number I can send you as many hard puzzles as you like.
You are right. I have also bought the Times, Guardian books etc. There is only a handful of really hard puzzles between them!
I have a computer program which checks them.
There are 3 types of hard puzzle.
They are all where the box converges on the row or columns.
There is a possibilty where only one number or even 2 numbers.
There is also another possibility. If you fax me I shall send you more details.
What ever you may read about on this forum, I can assure you Sudoku puzzles are very easy to compile and grade.
Most books are written by authors who have a only a very superficial knowledge of the subject and I don't just mean Carol Vorderman.
The last two puzzles in her book are the only real hard ones.
They use one of the 3 hard rules.

Be afraid ... be very afraid.

Pi wrote:

george-no1 wrote:Try this one, which many solvers are stumped on:

| . . . | . 7 . | 9 4 . |
| . 7 . | . 9 . | . . 5 |
| 3 . . | . . 5 | . 7 . |
+-------+-------+----
| . 8 7 | 4 . . | 1 . . |
| 4 6 3 | . . . | . . . |
| . . . | . . 7 | . 8 . |
+-------+-------+---
| 8 . . | 7 . . | . . . |
| 7 . . | . . . | . 2 8 |
| . 5 . | 2 6 8 | . . . |

G

I entered that one into Pappocom sudoku and it said it was invalid

The vast majority of actually difficult Sudoku's will be labeled "invalid" or "arguably unfair" by Pappocom. This is by design. He explains why within his software's help system.

Regardless, this puzzle is *objectively* valid. It has one and only one solution and if you're clever enough, you can find it in a logical manner.

| 2 1 5 | 8 7 6 | 9 4 3 |
| 6 7 8 | 3 9 4 | 2 1 5 |
| 3 4 5 | 1 2 5 | 8 7 6 |
+-------+-------+----
| 5 8 7 | 4 3 2 | 1 6 9 |
| 4 6 3 | 9 8 1 | 7 5 2 |
| 1 9 2 | 6 5 7 | 3 8 4 |
+-------+-------+---
| 8 2 6 | 7 4 3 | 5 9 1 |
| 7 3 4 | 5 1 9 | 6 2 8 |
| 9 5 1 | 2 6 8 | 4 3 7 |

Yeah - thanks gothenburg - we can all do that - but HOW did you do it.... that's what this forum is all about.

stuartn

george-no1 wrote:Try this one, which many solvers are stumped on:

| . . . | . 7 . | 9 4 . |
| . 7 . | . 9 . | . . 5 |
| 3 . . | . . 5 | . 7 . |
+-------+-------+----
| . 8 7 | 4 . . | 1 . . |
| 4 6 3 | . . . | . . . |
| . . . | . . 7 | . 8 . |
+-------+-------+---
| 8 . . | 7 . . | . . . |
| 7 . . | . . . | . 2 8 |
| . 5 . | 2 6 8 | . . . |

G

Actually, the number 8 on the last row (column 6) isn't needed, there is still only one possible sollution without it.

I know this thread is ancient, but I was searching for something and stumbled across it. The puzzle you posted can be simplified even more:

Code: Select all

...|.7.|94.
.7.|.9.|..5
3..|..5|.7.
-----------
...|4..|1..
463|...|...
...|..7|.8.
-----------
8..|...|...
7..|...|.28
.5.|26.|...


As to how I know it has a unique solution. just bung it in a brute force solver. Basically try every cell and any cell where all but one of the candidates leads to an invalid puzzle, you can fill. It's not pretty but it lets you know if a puzzle has a unique solution or not.

As for solving it by hand, I probably wouldn't try.

Dinarius wrote:Have you tried the Evil puzzles here?

http://www.websudoku.com/?level=4

D.

Code: Select all

 *-----------*
 |7..|.94|...|
 |..1|...|82.|
 |84.|...|...|
 |---+---+---|
 |5..|6..|.3.|
 |...|.12|...|
 |.1.|..3|..5|
 |---+---+---|
 |...|...|.13|
 |.84|...|7..|
 |...|95.|..6|
 *-----------*

salved with an grope of 12 friends

barneyzhen's puzzle is nice and easy.
But i agree with ab, his minimal version of Supersonic's puzzle seems to be so tough, that solving it manually probably is more work than fun.

Just for the heck of it . . .

Code: Select all

...|...|94.
...|.9.|..5
3..|..5|.7.
---+---+---
..7|4..|1..
463|...|...
...|..7|.8.
---+---+---
8..|7..|...
7..|...|.28
.5.|26.|...


This is the most reduced form.
Cheers