## AB Sudoku games. Are these games hard enough?

Everything about Sudoku that doesn't fit in one of the other sections

### AB Sudoku games. Are these games hard enough?

Hello everyone! Try to solve these games. I would appreciate if you evaluate them.

Game 1

6-----7--
---9-----
-4------3
83-2-----
--6---18-
-9---7---
---5---9-
7--12--6-
--4-6--57

Game 2
---1-74--
4---2----
6---5--1-
8--2-----
---765--3
-1--8--62
-------3-
3-2--98--
------9-7

Game 3

-----9-73
-2--3----
4-----6-5
-12------
36--24-81
-----6---
7----2--9
8-1------
---8-1-6-
Ab-ins

Posts: 3
Joined: 08 December 2005

Hello

Have tried them all. No. 1 is definitely the hardest - got stuck on that one at this point:

Code: Select all
`  *-----------* |6..|...|7..| |..7|9..|...| |.4.|7..|..3| |---+---+---| |835|2.1|.7.| |.76|...|18.| |.9.|687|.3.| |---+---+---| |.6.|57.|.91| |75.|12.|.6.| |..4|.6.|.57| *-----------*{6}     {128}   {12389} {348}   {1345}  {2358}  {7}     {124}   {589}   {1235}  {128}   {7}     {9}     {1345}  {23568} {568}   {124}   {568}   {1259}  {4}     {1289}  {7}     {15}    {2568}  {5689}  {12}    {3}     {8}     {3}     {5}     {2}     {49}    {1}     {469}   {7}     {469}   {24}    {7}     {6}     {34}    {3459}  {35}    {1}     {8}     {249}   {124}   {9}     {12}    {6}     {8}     {7}     {45}    {3}     {245}   {23}    {6}     {238}   {5}     {7}     {348}   {2348}  {9}     {1}     {7}     {5}     {389}   {1}     {2}     {3489}  {348}   {6}     {48}    {1239}  {128}   {4}     {38}    {6}     {389}   {238}   {5}     {7}     `

I guess it needs a forcing chain or something else that I still struggle with - would appreciate someone giving a hint for the next step!

No. 2 was reasonably challenging and I got to use the BUG principle for the first time which was satisfying. No. 3 fairly straightforward.

A good selection.
CathyW

Posts: 316
Joined: 20 June 2005

For #1, <Rubylips' solver> spots the following chain ...
r5c9~9~r1c9-9-r1c3-3-r2c1~3~r7c1~2~r5c1-2-r5c9
... so r5c9 cannot be 9, and that seems to do the trick.

Edit: Add the following:
For #2, there's a simple reduction based on row-candidates, after preliminary simple moves ...
Code: Select all
` 2    3    8    | 1    9    7    | 4    5    6     4    5    1    | 68   2    68   | 3    7    9     6    9    7    | 4    5    3    | 2    1    8    ----------------+----------------+-------------- 8    67   56   | 2    3    1    | 57   9    4     9    2    4    | 7    6    5    | 1    8    3     57   1    3    | 9    8    4    | 57   6    2    ----------------+----------------+-------------- 17   48   9    | 58   147  2    | 6    3    15    3    67   2    | 56   17   9    | 8    4    15    15   48   56   | 3    14   68   | 9    2    7    `

There are only three possible candidate-rows for r7:
1-4-9-8-7-2-6-3-5 (a)
7-4-9-8-1-2-6-3-5 (b)
7-8-9-5-4-2-6-3-1 (c)
There are only two possible candidate-rows for r8:
3-7-2-6-1-9-8-4-5 (a)
3-6-2-5-7-9-8-4-1 (b)
The only compatible candidate-rows for r7 & r8 are
r7(b): 7-4-9-8-1-2-6-3-5
r8(b): 3-6-2-5-7-9-8-4-1
and
r7(c): 7-8-9-5-4-2-6-3-1
r8(a): 3-7-2-6-1-9-8-4-5
therefore r7 & r8 reduce to
r7 = 7-48-9-58-14-2-6-3-15
r8 = 3-67-2-56-17-9-8-4-15
and the solution follows with simple moves.
Last edited by r.e.s. on Thu Dec 22, 2005 4:54 pm, edited 1 time in total.
r.e.s.

Posts: 337
Joined: 31 August 2005

CathyW wrote:Hello

Have tried them all. No. 1 is definitely the hardest - got stuck on that one at this point:

I guess it needs a forcing chain or something else that I still struggle with - would appreciate someone giving a hint for the next step!

No. 2 was reasonably challenging and I got to use the BUG principle for the first time which was satisfying. No. 3 fairly straightforward.

A good selection.

Glad that you like it! You can generate more games with this tool.
http://www.abinsight.com/sudoku/default.htm

One more challenging:
Code:
+---+---+---+
|89.|..2|.3.|
|2..|...|46.|
|1..|...|.7.|
|---+---+---|
|...|.2.|...|
|.6.|1.7|...|
|...|...|38.|
|---+---+---|
|.2.|6.4|7..|
|..4|..9|5..|
|93.|..8|...|
+---+---+---+
Ab-ins

Posts: 3
Joined: 08 December 2005

Thanks for tip on the first puzzle - personally not that keen on those that require forcing chains as I still haven't worked out where best to start looking for them.

Last one also too hard for me. I had to resort to Susser (Simple Sudoku and Sadman Sudoku got stuck too!) and ask the programme to deduce next steps. When it comes to Nishio cycles and forcing chains (other than the simplest x-y wing) I'm afraid I lose interest.
CathyW

Posts: 316
Joined: 20 June 2005

Ab-ins wrote:You can generate more games with this tool.
http://www.abinsight.com/sudoku/default.htm

An exe file of more than 25MB!?
r.e.s.

Posts: 337
Joined: 31 August 2005

r.e.s. wrote:
Ab-ins wrote:You can generate more games with this tool.
http://www.abinsight.com/sudoku/default.htm

An exe file of more than 25MB!?

I apologize for the 25mb setup file size as it includes Microsoft .NET 2.0 Framework.
I'm planning to build AB Sudoku for Microsoft Windows Mobile. That mobile version will only include the solver part, so you will have to download generated games from your PC. I don’t want to include generator because of limited CPU resources of mobile devices. Is it a valuable point on your opinion?
Ab-ins

Posts: 3
Joined: 08 December 2005

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