The New Sudoku Players' Forum

[lath]

This puzzle looks way too hard...look how few givens there are in the lower part of the puzzle! So far I've only been able to solve puzzles that are fairly easy, like naked singles and hidden doubles.

Please help, thanks!

[Condor]

Hi lath

Have a look at row 4. There is a naked triple.

Also have a look at column 4

[lath]

Hi, thanks for the tips. I'll still probably be at this one for a while...still trying to get used to this game, it's addicting.

Would you agree that his puzzle is difficult? Or how would you rate it?

Thanks.

[fermat]

Would you agree that his puzzle is difficult? Or how would you rate it?

Thanks.

It is too hard for me to solve without computer help, but there are several people here who can.

Sudoku Explainer rates it a 7.1 out of 10.

Code: Select all

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


[ravel]

One possible solution (r5c4=3, r4c3=3, r4c8=6):
r9c6=6 => r7c4=8
r9c7=6 => r7c7=1 => r7c9=5 => r7c4=8

[udosuk]

Code: Select all

 *-----------------------------------------------------------------------------*
 | 6       1       47      | 2       3       8       | 4579    479     4579    |
 | 5       9       8       | 4       6       7       | 3       1       2       |
 | 3       47      2       | 1       9       5       | 47      8       6       |
 |-------------------------+-------------------------+-------------------------|
 | 149     5       3       | 7       14      2       | 8       6       49      |
 | 24789   2467    4679    | 3       48      469     | 2479    5       1       |
 | 124789  2467    4679    | 68      5       1469    | 2479    3       479     |
 |-------------------------+-------------------------+-------------------------|
 | 249     3       469     |*68      7       146     |*14569   249    *4589    |
 | 2479    2467    1       | 5       248     3       | 4679    2479    4789    |
 | 247     8       5       | 9       124    *146     |*1467    247     3       |
 *-----------------------------------------------------------------------------*

Another way to express ravel's move is the simple forcing chain:
[r7c4]=8=[r7c9]=5=[r7c7]=1=[r9c7]=6=[r9c6]-6-[r7c4]

r7c4=6 => r7c9=8 => r7c7=5 => r9c7=1 => r9c6=6

So r7c4<>6, r7c4=8...

I think this puzzle is too hard for non-advanced players...

[freestyleses]

I'm far from an advanced player, BUT, r9c9 is a 3 since 3 can be excluded from r7c9 since either r7c2 or r7c3 is a 3. make sense? sorry, i don't know all the sudoku lingo.

don't think it gets you anywhere though.

[Albatros]

This puzzle looks way too hard...look how few givens there are in the lower part of the puzzle! So far I've only been able to solve puzzles that are fairly easy, like naked singles and hidden doubles.

Please help, thanks!

I am new to this sudoko puzles so bear in mind that i could be wrong.

I think that it has multiple solutions based on 2 main lines:

The first one is:

6 -----1------*47------2------3------8-------5------9-------*47

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

3------2-------*47-----1------9------5------*47-----8 -----6


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

2----*47-----6-------3------8------9------*47----5------- 1

8-----*47----9-------6------5------1------2------3-----*47



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

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


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



From this first box you get two solutions. Choose number 4 or 7 in one box marked with an * and fill the rest accordingly.

The second main "line" has even more than two correct solutions. Here it is:



6 1 *47, 2 3 8 5 *479, *79,

5 9 2 4 6 7 3 1 8

3 *47, 8 1 9 5 *247, *247, 6


9 5 3 7 1 2 8 6 4

8 *27, *67, 3 4 *69, *279, 5 1

1 *247, *467, 8 5 *69, *2479, 3 *279,


2 3 9 6 7 4 1 8 5

*47, 6 1 5 8 3 *2479, *2479, *279,

*47, 8 5 9 2 1 6 *47, 3

[udosuk]

I am new to this sudoko puzles so bear in mind that i could be wrong.

I think that it has multiple solutions based on 2 main lines...

Yes, you're wrong. This puzzle has a unique solution as below:

Code: Select all

617238594
598467312
342195786
153742869
476389251
829651437
934876125
761523948
285914673

Prove me wrong if you can provide another different solution...

[RW]

The first one is:

6 -----1------*47------2------3------8-------5------9-------*47

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

3------2-------*47-----1------9------5------*47-----8 -----6

...

The underlined '2' is in column 3 in the original.

RW

[daj95376]

One possible solution (r5c4=3, r4c3=3, r4c8=6):
r9c6=6 => r7c4=8
r9c7=6 => r7c7=1 => r7c9=5 => r7c4=8

I spent last night scanning all of the posts in the Programmers Forum looking for information on chains that I could understand and put to use. One of the threads was on Double Implication Chains ... and here is a perfect example of one. On top of that, udosuk posted a simple Forcing Chain equivalent ... along with an equivalent sequence in =>'s.

Thanks ravel and udosuk!!!

[Albatros]

I am new to this sudoko puzles so bear in mind that i could be wrong.

I think that it has multiple solutions based on 2 main lines...

Yes, you're wrong. This puzzle has a unique solution as below:

Code: Select all

617238594
598467312
342195786
153742869
476389251
829651437
934876125
761523948
285914673

Prove me wrong if you can provide another different solution...

You are right. I copied one number from the original given numbers in the wrong square.

[sweetbix]

Code: Select all

 *---------------------------------------------------------------------------*
 | 6       1       47      | 2       3       8       | 4579    479     4579  |
 | 5       9       8       | 4       6       7       | 3       1       2     |
 | 3       47      2       | 1       9       5       | 47      8       6     |
 |-------------------------+-------------------------+-----------------------|
 | 149     5       3       | 7       14      2       | 8       6       49    |
 | 24789   2467    4679    | 3       48      469     | 2479    5       1     |
 | 124789  2467    4679    | 68      5       1469    | 2479    3       479   |
 |-------------------------+-------------------------+-----------------------|
 | 249     3       469     |*68      7       146     |*14569   249    *4589  |
 | 2479    2467    1       | 5       248     3       | 4679    2479    4789  |
 | 247     8       5       | 9       124    *146     |*1467    247     3     |
 *---------------------------------------------------------------------------*

Another way to express ravel's move is the simple forcing chain:
[r7c4]=8=[r7c9]=5=[r7c7]=1=[r9c7]=6=[r9c6]-6-[r7c4]

r7c4=6 => r7c9=8 => r7c7=5 => r9c7=1 => r9c6=6

So r7c4<>6, r7c4=8...

Hi udosuk, can you explain this to me?
I get r7c4=6 => r7c9=8 => r7c7=5 => r9c7=1 => r9c6=4

Thanks.

[ravel]

Both is correct:
r9c6=6 follows, because it is the last cell in row 9 with a 6.
r9c6=4 follows, because there is a 6 in box 8 and a 1 in row 9.
This is just another contradiction.

[daj95376]

sweetbix,

I suspect that you have the same problem that I (and my solver) have with chains. You actually perform the assigments/eliminations while following a chain. I've learned, as this example demonstrates, that chains are a hypothetical sequence of events and no actual assignments/eliminations occur until a conclusion is reached.

If you actually do make assignments/eliminations while working with this chain, then you need to examine [r9] for <6> after making the [r9c7]=1 assignment. You end up with [r9]=INVALID ... and this invalidates your premise that [r7c4]=6.