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March 2 bundle

 
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Sun Mar 02, 2008 11:01 am    Post subject: March 2 bundle Reply with quote

these were posted on sudoku.org.uk


#966

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

=================

weekly extreme # 75

Code:
+-------+-------+-------+
| . . . | . 6 8 | . . . |
| . 2 . | 7 . 9 | . 1 . |
| . . 1 | . . . | . . 4 |
+-------+-------+-------+
| . 5 7 | 6 . . | . 9 . |
| 2 . . | . 8 . | . . 1 |
| . 1 . | . . 7 | 5 4 . |
+-------+-------+-------+
| 5 . . | . . . | 4 . . |
| . 9 . | 5 . 6 | . 3 . |
| . . . | 4 7 . | . . . |
+-------+-------+-------+ SE 8.4

================

daily telegraph-Feb 29

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

================

the opening moves to the extreme are an x-wing then an xy-wing... then??

the telegraph is a one stepper.


Last edited by storm_norm on Mon Mar 03, 2008 5:40 am; edited 1 time in total
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Marty R.



Joined: 12 Feb 2006
Posts: 5061
Location: Rochester, NY, USA

PostPosted: Sun Mar 02, 2008 4:28 pm    Post subject: Reply with quote

Norm, I know the first two puzzles are the Friday and Sunday diabolicals that I still refer to as Mepham, even though he's gone. Is the extreme from the same source, one level harder than the diabolical?
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Marty R.



Joined: 12 Feb 2006
Posts: 5061
Location: Rochester, NY, USA

PostPosted: Sun Mar 02, 2008 6:41 pm    Post subject: Reply with quote

Quote:
the opening moves to the extreme are an x-wing then an xy-wing... then??


After that I eliminated one candidate to break up a deadly pattern. Then a couple of iterations of extended Medusa and that did it.
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Sun Mar 02, 2008 8:16 pm    Post subject: Reply with quote

marty,

I am not exactly sure of all the details, but it looks like Andrew Stuart has been leading the way for that site to hold these competitions. and from what I have been reading, he has several competition puzzles going on all the time, including the daily and the weekly extremes. so I am assuming that Andrew Stuart is the one coming up with the puzzles.
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keith



Joined: 19 Sep 2005
Posts: 3136
Location: near Detroit, Michigan, USA

PostPosted: Sun Mar 02, 2008 9:27 pm    Post subject: Reply with quote

The first puzzle, #964, is discussed here:

http://www.dailysudoku.com/sudoku/forums/viewtopic.php?t=2391

Keith
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storm_norm



Joined: 18 Oct 2007
Posts: 1741

PostPosted: Mon Mar 03, 2008 5:39 am    Post subject: Reply with quote

keith wrote:
The first puzzle, #964, is discussed here:

http://www.dailysudoku.com/sudoku/forums/viewtopic.php?t=2391

Keith



oops, ok, I will take it out.
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keith



Joined: 19 Sep 2005
Posts: 3136
Location: near Detroit, Michigan, USA

PostPosted: Mon Mar 03, 2008 6:45 am    Post subject: Reply with quote

storm_norm wrote:
oops, ok, I will take it out.

No need to do that. Just so people have the cross-reference.

Keith
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Asellus



Joined: 05 Jun 2007
Posts: 865
Location: Sonoma County, CA, USA

PostPosted: Tue Mar 04, 2008 10:46 am    Post subject: Reply with quote

I had encountered this "Extreme" puzzle before it was posted here and solved it exactly as Marty described above. However, this posting prompted me to revisit it and see what I could do if I avoided any use of extended Medusa. It made for a nice study in AICs. Those wishing to explore AICs might want to follow along. (I don't claim this is the most elegant solution. But, I found it interesting.) I number the steps in brackets, for those keeping count.

After basics plus: [1] the X-Wing on <8> in c28; [2] the XY Wing with r6c9 pivot that removes <7> from r7c8; and [3] the r79c38 {26} UR that removes <2> from r9c8, we have:
Code:

+-----------------+-------+------------------+
| 3479  347  3459 | 1 6 8 | 2379  257  23579 |
| 368   2    3568 | 7 4 9 | 368   1    3568  |
| 679   678  1    | 3 5 2 | 679   678  4     |
+-----------------+-------+------------------+
| 38    5    7    | 6 1 4 | 238   9    238   |
| 2     346  346  | 9 8 5 | 367   67   1     |
| 689   1    689  | 2 3 7 | 5     4    68    |
+-----------------+-------+------------------+
| 5     367  236  | 8 9 1 | 4     26   267   |
| 1478  9    48   | 5 2 6 | 178   3    78    |
| 16    68   26   | 4 7 3 | 1269  568  2569  |
+-----------------+-------+------------------+

[4] I started by looking for exploitable ALSs and quickly noticed an interesting possiblity in the middle floor that led to a nice branched AIC:
Code:

                      ({67})r5c78=(3)r5c7
                  /                         \
(8)r2c9-(8=9)r6c9                             (3={68})r2c17-(8)r2c9; r2c9<>8
                  \                         /
                    (6={89})r6c13-(8=3)r4c1

Notice how the two branches knock out the two <3>s in the {368} ALS in r2.

[5] Note that the 2 <8>s in r4 of b6, considered as a group, are strongly linked with the <8> in r6c9. We can exploit this in a chain:


(3)r5c3-(3=8)r4c1-(8)r4c13=(8)r6c9-(8=7)r8c9-(7)r7c9=(7-3)r7c2=(3)r7c3-(3)r5c3; r5c3<>3

[6] We have now exposed a {468} XY Wing, pivot r8c3, that removes <6> from r5c2 and r79c3.

The grid now:
Code:

+----------------+-------+------------------+
| 3479  34   459 | 1 6 8 | 2379  257  23579 |
| 368   2    568 | 7 4 9 | 368   1    356   |
| 679   678  1   | 3 5 2 | 679   678  4     |
+----------------+-------+------------------+
| 38    5    7   | 6 1 4 | 238   9    238   |
| 2     34   46  | 9 8 5 | 367   67   1     |
| 689   1    689 | 2 3 7 | 5     4    68    |
+----------------+-------+------------------+
| 5     67   3   | 8 9 1 | 4     26   267   |
| 1478  9    48  | 5 2 6 | 178   3    78    |
| 16    68   2   | 4 7 3 | 169   568  569   |
+----------------+-------+------------------+

[7] There is now an AIC that exploits some strong links in <8>, <4> and <3> with a couple of bivalues along the way. Some Medusa multi-coloring helped me find it.

(3-8)r2c7=(8)r3c8-(8=8)r9c28-(8=4)r8c3-(4)r5c3=(4-3)r5c2=(3)r5c7-(3)r2c7; r2c7<>3

[8] This exposes a {68} W-Wing in b37, based on the strongly linked <8>s in c8, that removes <6> from r9c7.

[9] It also exposes an otherwise useless XYZ Wing in r2c7|r35c8. We can transport the <6>s in r35c8 to r79c9 (by grouped strong links). This eliminates <6> from r2c9. (NOTE: I don't believe that this step is necessary for the solution. However, I included it because it is not an AIC and is interesting.)

[10] With <3> gone from r2c7, we have another AIC (which Medusa multi-coloring could find):

(8-5)r2c3=(5-3)r2c9=(3)r2c1-(3)r4c1=(3-4)r5c2=(4)r5c3-(4=8)r8c3-(8)r2c3; r2c3<>8

[11] Now that r2c3 is a {56} bivalue, we can exploit it in another AIC:

(5)r1c3-(5=6)r2c3-(6=8)r2c7-(8)r3c8=(8-5)r9c8=(5)r1c8-(5)r1c3; r1c3<>5

The grid now:
Code:

+----------------+-------+---------------+
| 3479  34   49  | 1 6 8 | 279  257  59  |
| 68    2    5   | 7 4 9 | 68   1    3   |
| 679   678  1   | 3 5 2 | 679  678  4   |
+----------------+-------+---------------+
| 38    5    7   | 6 1 4 | 238  9    28  |
| 2     34   46  | 9 8 5 | 367  67   1   |
| 689   1    689 | 2 3 7 | 5    4    68  |
+----------------+-------+---------------+
| 5     67   3   | 8 9 1 | 4    26   267 |
| 1478  9    48  | 5 2 6 | 178  3    78  |
| 16    68   2   | 4 7 3 | 19   568  59  |
+----------------+-------+---------------+

[12] There is another otherwise useless XYZ Wing in r2c1|r37c2. We can transport the <6>s in r37c2 to r9c1, thus removing <6> from r36c1. Notice that a naked quad in b1 now removes <7> from r3c2, resulting in some more simplification:
Code:

+---------------+-------+--------------+
| 3479  34  49  | 1 6 8 | 279  257  59 |
| 68    2   5   | 7 4 9 | 68   1    3  |
| 79    68  1   | 3 5 2 | 679  678  4  |
+---------------+-------+--------------+
| 38    5   7   | 6 1 4 | 238  9    28 |
| 2     34  46  | 9 8 5 | 367  67   1  |
| 89    1   689 | 2 3 7 | 5    4    68 |
+---------------+-------+--------------+
| 5     7   3   | 8 9 1 | 4    26   26 |
| 148   9   48  | 5 2 6 | 18   3    7  |
| 16    68  2   | 4 7 3 | 19   58   59 |
+---------------+-------+--------------+

[13] Next is an XY Chain, from r2c7 via b1, c2, r9 and b9 to r8c7. Or, perhaps more elegantly, it can be seen as a {68} remote pair, r2c7 and r9c2, extended by the <8> strong link in b9. In either case, it removes <8> from r4c7.

[14] Unless someone can see something I cannot, we need one more AIC:

(8)r68c1-(8=6)r2c1-(6)r3c2=(6-8)r9c2=(8-5)r9c8=(5-2)r1c8=(2)r1c7-(2=3)r4c7-(3=8)r4c1-(8)r68c1; r68c1<>8

This solves the puzzle.
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