mersenneforum.org  

Go Back   mersenneforum.org > Fun Stuff > Puzzles

Reply
 
Thread Tools
Old 2008-03-20, 04:52   #1
JuanTutors
 
JuanTutors's Avatar
 
"Juan Tutors"
Mar 2004

571 Posts
Default Sudoku puzzle help

I'm having a hell of a time with this sudoku puzzle. I've never gotten to a point that a puzzle would take me even close to an hour, except for this puzzle.

What I would like from you puzzle geniuses:

1. I'm pretty sure there are no mistakes. I checked it over. But If I made an error, tell me what it is.

2. Otherwise, find a number and tell me how you found it.

The black numbers are the numbers the puzzle came with. The grey numbers are the numbers I entered.

http://www.ourspacer.com/misc/sudoku.jpg
JuanTutors is offline   Reply With Quote
Old 2008-03-20, 05:14   #2
retina
Undefined
 
retina's Avatar
 
"The unspeakable one"
Jun 2006
My evil lair

5·1,321 Posts
Default

My solver program shows it is solvable:

358617924
267489351
941325786
482753169
736891245
519264873
875936412
123548697
694172538


I have no idea how it solved it though :(
retina is online now   Reply With Quote
Old 2008-03-20, 05:56   #3
markr
 
markr's Avatar
 
"Mark"
Feb 2003
Sydney

3×191 Posts
Default

The cell in the lower-left corner is 6. From there it falls out.

I got to where you did no problem, then was lucky with a method I'm just starting to get the hang of. If you look at the five cells highlighted blue, they all have just two possible numbers, and form a chain (3,7) (7,1) (1,3) (3,1) (1,3). If the first cell is not 3, it's 7, so the next cell in the chain is 1, and so on until the last one is 3. Either way, at least one end of the chain is a 3. So the lower-left-corner cell can't be 3, leaving just one possibility.

There's probably other ways to get to the solution.
Attached Thumbnails
Click image for larger version

Name:	sudoku_from_forum_chain.gif
Views:	142
Size:	20.7 KB
ID:	2333  
markr is offline   Reply With Quote
Old 2008-03-20, 11:32   #4
Kees
 
Kees's Avatar
 
Dec 2005

22×72 Posts
Default

http://www.scanraid.com/sudoku.htm
Kees is offline   Reply With Quote
Old 2008-03-20, 19:20   #5
petrw1
1976 Toyota Corona years forever!
 
petrw1's Avatar
 
"Wayne"
Nov 2006
Saskatchewan, Canada

32×7×83 Posts
Default YES.... this is the one I use when all else fails.

http://www.scanraid.com/sudoku.htm

It is by far the smartest "I have found" so far .... meaning I haven't checked out every one (by no means) but when I found this one I was impressed.

It has many VERY advanced techniques and as a bonus it has links to describe these techniques ... AND ... if all else fails it has links to another very advanced site complete with a forum.

Go crazy ....
petrw1 is offline   Reply With Quote
Old 2008-03-21, 01:10   #6
Fusion_power
 
Fusion_power's Avatar
 
Aug 2003
Snicker, AL

17008 Posts
Default

When I first saw this one I hoped it would be really hard. It took about 20 minutes.

It is VERY susceptible to chain analysis.

DarJones
Fusion_power is offline   Reply With Quote
Old 2008-03-21, 01:43   #7
Fusion_power
 
Fusion_power's Avatar
 
Aug 2003
Snicker, AL

26×3×5 Posts
Default

Just so an explanation is given for the problem posed, here is the way it should be analyzed.

Look at cell A5. This is the cell at top center. Only two possibilities can fit, either 1 or 7. Regardless of what value you put in this cell, the only value that can possibly fit in cell I1 is 6. This is the cell at the bottom left corner. You can find this referred to as a "forced chain".

There is one other way to analyze this but the above is the simplest.

DarJones
Fusion_power is offline   Reply With Quote
Old 2008-03-21, 04:22   #8
JuanTutors
 
JuanTutors's Avatar
 
"Juan Tutors"
Mar 2004

571 Posts
Default

I'll look up this article on sudoku. I like coming up w/ the tricks myself, but I never learned this "forced chain" concept. I've used it before, but it never seemed so viable. Maybe there's a smart way of knowing where to start looking? I don't use notes.
JuanTutors is offline   Reply With Quote
Old 2008-03-21, 15:17   #9
davieddy
 
davieddy's Avatar
 
"Lucan"
Dec 2006
England

2·3·13·83 Posts
Default

Quote:
Originally Posted by retina View Post
My solver program shows it is solvable:

I have no idea how it solved it though :(
Brute force (and ignorance)?

Last fiddled with by davieddy on 2008-03-21 at 15:50
davieddy is offline   Reply With Quote
Old 2008-03-21, 15:20   #10
davieddy
 
davieddy's Avatar
 
"Lucan"
Dec 2006
England

194A16 Posts
Default

Quote:
Originally Posted by Fusion_power View Post
Just so an explanation is given for the problem posed, here is the way it should be analyzed.

There is one other way to analyze this but the above is the simplest.

DarJones
See Markr's post for a very clear description of the "chain".

Only one other way? What is it?
davieddy is offline   Reply With Quote
Old 2008-03-21, 15:31   #11
retina
Undefined
 
retina's Avatar
 
"The unspeakable one"
Jun 2006
My evil lair

147158 Posts
Default

Quote:
Originally Posted by davieddy View Post
Brute force?
I expect so. This computer is a brute, if I drop it on my toe it won't say sorry.
retina is online now   Reply With Quote
Reply

Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
a partial sudoku puzzle MattcAnderson Miscellaneous Math 4 2017-06-29 07:14
An auto-eroica sudoku Batalov Puzzles 21 2015-06-24 10:24
Sodyoutoo (a.k.a. Sudoku) mwxdbcr Puzzles 15 2015-05-17 05:27
a puzzle bcp19 Puzzles 18 2012-03-02 04:11
Dot puzzle nibble4bits Puzzles 37 2006-02-27 09:35

All times are UTC. The time now is 14:18.


Thu Oct 6 14:18:34 UTC 2022 up 49 days, 11:47, 0 users, load averages: 1.73, 1.48, 1.39

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2022, Jelsoft Enterprises Ltd.

This forum has received and complied with 0 (zero) government requests for information.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation.
A copy of the license is included in the FAQ.

≠ ± ∓ ÷ × · − √ ‰ ⊗ ⊕ ⊖ ⊘ ⊙ ≤ ≥ ≦ ≧ ≨ ≩ ≺ ≻ ≼ ≽ ⊏ ⊐ ⊑ ⊒ ² ³ °
∠ ∟ ° ≅ ~ ‖ ⟂ ⫛
≡ ≜ ≈ ∝ ∞ ≪ ≫ ⌊⌋ ⌈⌉ ∘ ∏ ∐ ∑ ∧ ∨ ∩ ∪ ⨀ ⊕ ⊗ 𝖕 𝖖 𝖗 ⊲ ⊳
∅ ∖ ∁ ↦ ↣ ∩ ∪ ⊆ ⊂ ⊄ ⊊ ⊇ ⊃ ⊅ ⊋ ⊖ ∈ ∉ ∋ ∌ ℕ ℤ ℚ ℝ ℂ ℵ ℶ ℷ ℸ 𝓟
¬ ∨ ∧ ⊕ → ← ⇒ ⇐ ⇔ ∀ ∃ ∄ ∴ ∵ ⊤ ⊥ ⊢ ⊨ ⫤ ⊣ … ⋯ ⋮ ⋰ ⋱
∫ ∬ ∭ ∮ ∯ ∰ ∇ ∆ δ ∂ ℱ ℒ ℓ
𝛢𝛼 𝛣𝛽 𝛤𝛾 𝛥𝛿 𝛦𝜀𝜖 𝛧𝜁 𝛨𝜂 𝛩𝜃𝜗 𝛪𝜄 𝛫𝜅 𝛬𝜆 𝛭𝜇 𝛮𝜈 𝛯𝜉 𝛰𝜊 𝛱𝜋 𝛲𝜌 𝛴𝜎𝜍 𝛵𝜏 𝛶𝜐 𝛷𝜙𝜑 𝛸𝜒 𝛹𝜓 𝛺𝜔