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Jun 28 VH

 
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ZeroAssoluto



Joined: 05 Feb 2017
Posts: 642
Location: Rimini, Italy

PostPosted: Mon Jun 28, 2021 7:32 am    Post subject: Jun 28 VH Reply with quote

Hi everyone,

Code:

+--------------+------------+------------+
| 269 1   49   | 8  39 3469 | 7   29 5   |
| 7   234 489  | 1  5  49   | 238 6  234 |
| 69  345 4589 | 2  7  469  | 1   89 34  |
+--------------+------------+------------+
| 8   45  459  | 39 2  1    | 6   35 7   |
| 3   6   1    | 7  4  5    | 28  28 9   |
| 29  25  7    | 6  8  39   | 4   35 1   |
+--------------+------------+------------+
| 4   7   2    | 5  39 8    | 39  1  6   |
| 1   9   3    | 4  6  2    | 5   7  8   |
| 5   8   6    | 39 1  7    | 239 4  23  |
+--------------+------------+------------+

Play this puzzle online at the Daily Sudoku site

Quote:
Skyscraper with number 9 in r2c36,r6c16 and -9 in r13c1,r4c3
or
Skyscraper with number 9 in r2c36,r4c34 and -9 in r6c6


Ciao Gianni
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TomC



Joined: 30 Oct 2020
Posts: 144
Location: Wales

PostPosted: Mon Jun 28, 2021 9:41 am    Post subject: Reply with quote

r1c6 <> 3 as then r1c1=6, r3c1=9, r1c5=9 leading to no 9's in box 3
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Mogulmeister



Joined: 03 May 2007
Posts: 970

PostPosted: Mon Jun 28, 2021 5:23 pm    Post subject: Reply with quote

Glory be! A fish. It is a swordfish for 9s in r136c16 r13c8

This swordfish has a fin at r2c6. It doesn't matter because whether the swordfish is true or the fin is true, the 9 in r1c5 is toast.
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peter urhegyi



Joined: 26 Oct 2020
Posts: 14

PostPosted: Tue Jun 29, 2021 7:37 am    Post subject: Daily sudoku Jun 28 VH Reply with quote

In case anyone will try the classical solution with only xy(z) wings requires 2 xyz-wings and 2 xy-wings that are all necessary to solve.
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Mogulmeister



Joined: 03 May 2007
Posts: 970

PostPosted: Tue Jun 29, 2021 10:29 am    Post subject: Reply with quote

Hi Peter - yes a v good point which is why (imho) wings are helpful but also should be augmented with different ways of looking at strong links.

This puzzle is great because it shows good examples of great alternatives to the classical approach if you take different looks at strong links - sometimes with more efficient solutions:

Pattern

1)Gianni's skyscrapers - the strong links on 9's in r24. They share a base in c3 so either r4c4 is 9 or r2c6 is 9 and r6c6 is <>9.

2)Finned swordfish for 9's and r1c5 <> 9

Observation/Inspection

3)TomC disrupting the strong link on 6's in r1. A 3 in r1c6 makes r1c5 a 9 and also makes r3c1 a 9 which means no 9's in box 3 = impossibility - so it is eliminated. Solved. That 3 in r1c6 is also part of a strong link with r6c6.
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dongrave



Joined: 06 Mar 2014
Posts: 450

PostPosted: Tue Jun 29, 2021 12:41 pm    Post subject: Re: Daily sudoku Jun 28 VH Reply with quote

peter urhegyi wrote:
In case anyone will try the classical solution with only xy(z) wings requires 2 xyz-wings and 2 xy-wings that are all necessary to solve.


That's how I solved it peter! (I wasn't sure if they were all necessary though.) I started with a 269 XYZ Wing (pivot at r1c1, -9r1c3), then a 234 XYZ Wing (pivot at r2c9, -3r2c7), then a 28-9 XY Wing (pivot at r2c7, -9r1c1), and finally a 26-9 XY Wing (pivot at r1c1, -9r3c8).
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