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Tough Sudoku for 5/April/2006


Choose a number, and place it in the grid above.

  1 2 3 4 5 6 7 8 9
Check out the latest post in the Sudoku Forum

Sudoku Solving Techniques

Submitted by: sudoku lover

Indicate which comments you would like to be able to see

to post or not?long time since i came here first or nearer to first.
so G mean all
post first puzzle later
Is that like 'To be, or not to be - that is the question?' From Shakespeare's play...
I hope someone tells us who is in the photo. Not Greg Norman, anyway
No mistakes, and no guessing on this one!
Maybe the next Tiger Woods?
Hello aussiemike if you are on here tonight. I haven't seen you post lately until last night. Hope all is well with you.
Ho hum - Golf lovers will probably find it fascinating!
catch them young eh?senior and junior playing golf.finished with a few guesses.didnt notice the time.took long.
and jenni you read my mind..
Tough for me today -- I had to make 4 guesses.

A great father - son moment!
Not cleaned and not optimized (and almost certainly can be improved): Simple Sudoku hints bring you to 31 filled. The Pigeonhole pattern
g8=9 g8=5 0000 0000 0000
0000 h7=5 h7=1 0000 0000
0000 0000 h9=1 e9=1 0000
g2=1 0000 0000 e2=1 d2=1
g2=5 0000 0000 0000 d2=5
eliminates g2=9. then UP to end.
At 31 filled, you can finish out a solution by using the unique rectangle in 27's in Chi => i3=9, but that doesn't constitute a proof that the solution is unique. (It assumes that the solution is unique.) Eliminating g2=9 or an equivalent step is much tougher. Simple Sudoku gives no hints at this point.
Andrei: Thank you. We crossed in submission. Wish I could 'see' the matrices as easily as you do.
Timer 00:09:02
Maen to all. For AP from India.... puzzle first and then post. Where's the glory in being first if you haven't competed?
what picture are you guys talking about? How do you go about solving the tough sudoku problems, I am sooooooo stuck!
mmm, Greg you got a point,generally i post only after completing and today i happen to see the page empty ,so thought will make a comment..thats it.. i claim no glory neither for commenting nor for completing
oh ho the name didnt get thru.that comment to Greg is from me
Say Andrei?

Do you have a description of this 'pigeonhole'-stuff somewhere on the internet?
after 31 filled there is a Deadly Rectangle in h5,i5,h3,i3 making i3=9. Easy fillings to 81. Pretty conclusive to me
Brooks: see my description of a Pigeonhole pattern
as a comment for the Tough April 3 puzzle.
24:04 Good mAen!
andrei could you explain the pigeonhole pattern
andrei will follow your comment above, i didn;t see it before
At 31 filled, eliminate h7=1 because if so:
e9=1, e8=9, g8=5, and g1=1
f3=6, so d1 has no possibilities left.
Easy to 81 filled.
A little over 8 minutes - and it looks like the Dad is going to whack his son to me! LOL
bill how about d1=5
Good mAen! Looks like a new golfer in training. No timer this time. Just the cake in the oven!
I'll bet junior sized left handed clubs are hard to come by!
My hat's off to the dad, though, not making the kid try to play right-handed.
Been there, done that.
4.23 today
Hi Mark - I think Bill left out a few steps:
The implied pair 27 at e1,e2 and the strong 5's in row 2 - thus d2=5. His proof is then depth 9 as it considers 9 strong sets:
1's in box e8, 9's in box e8, 59 at g8, 15 at g1, 127 at e1, 127 at e2, 276 at f3, 5's in row 2,d1=12567.
Here is my take on today's puzzle:
It is pared down to the fewest sets I needed, inho - a total of nine sets.

1) Start at 22 filled - the given puzzle. UP to 24.
2) Hidden pair 27 at hi5 forbids 2 at def5, forbids 7 at def5, forbids 4 at hi5, forbids 5 at hi5, forbids 6 at i5. UP More...
I think that Simple Sudoku uses more sets than 9 - about 17 or so, just to get stuck at 31 filled - compared to a human solution which uses only 9 sets to solve the entire puzzle!

I think I have begun to appreciate the value in looking for efficiency as taught by gb.
Hi Everyone,

Just put in a new feature so that you can enter your numbers with the keyboard, not just the mouse. Let me know what you think.

Love that photo! I really enjoy seeing dads with their sons. (I'm assuming here of course)
Hi Everyone,

I just wanted to add - Thank you to everyone who took the time to write their suggestions for improvements, either here or via email. I try to respond to everyone who sends an email, but I know a few of these have got past me. I'm steadily making my way through the list.

how's the kid gonna swing?
Even though I'm not a golfer, it's a great father-son picture.
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