I found this one much harder than usual.  It took me 26 minutes; a gentle or moderate normally takes well under 20 minutes.

On checking the solutions this evening I see that I wasn't the only one who found it hard.  The average time was 44 minutes with about 30 fewer than usual correct solutions submitted.

The key to this puzzle is column 1.

Innie/outie difference on column 1 gives r1c2-r6c1=6.

But we know 8 is already placed in r1, and 3 is already easily placed in c1 at r5c1 (outie of r1234).

So the only possible combination is r1c2=7, r6c1=1.

The rest follows easily from here.

Time to solve : 12 minutes

Angel:

Angel: If, according to you, the: Innie/outie difference on column 1 = 6

 r1c2 and r6c1=6

Why would the only possible combination = 8 ?

 r1c2=7 r6c1=8

Jeannette, I am talking about a difference between r1c2 and r6c1 - ie a subtraction.

Consider column 1:

We know that column 1 must add to 45
So working downwards (18-r1c2)+14+r6c1+19=45
This gives us our innie/outie difference of 6, ie r1c2-r6c1=6

The only ways to get a difference of 6 are:

9-3 (not possible as c1 already has a 3)
8-2 (not possible as r1 already has an 8)
7-1

So we place 7 in r1c2, we place 1 in r6c1

This method is often very useful - if the difference is 8 for instance you know you can place a 9 and a 1 immediately. On the other hand if the difference is only 1 (as it happens to be in column 9 of this puzzle) you need a lot of other information as well.

Thanks Angel:

I'm still not getting it, but I will work on it.

Hi Jeannette

Sorry - I'll try again.

I think it is clear that r5c1 must be 3, obtained by r5c1 being an outie of r1234.

All 9 cells of column 1 must total 45. But we can also say that the total for column 1 can be obtained by adding all the complete cages and all the 'extra' bits from other cages. In other words the total for column 1 can be obtained by adding:

complete cages 14(3) and 19(3) and 'extra' cells r1c1, r2c1 and r6c1

this is the same as 33 + 'extra' cells r1c1, r2c1 and r6c1

but we see that r1c1 and r2c1 are both part of an 18(3) cage with
r1c1 + r2c1+ r1c2 = 18

so we can say that r1c1 + r2c1 = 18 - r1c2

so now our 'extra' cells can be expressed as 18 - r1c2 and r6c1

so looking at column 1 as a whole we have

33 + 18 - r1c2 + r6c1 = 45

ie 51 - r1c2 + r6c1 = 45

ie 6 + r6c1 = r1c2

that is r1c2 must be 6 more than r6c1

Since we can only use the numbers 1 to 9, there are only 3 ways that we can get a pair of numbers where one is 6 more than the other:

r1c2=9 and r6c1=3
r1c2=8 and r6c1=2
r1c2=7 and r6c1=1

But only the last of these does not conflict with already known placements (since we have r5c1=3 and r1c5=8)

Apologies if I've rambled on a bit here, or if I've missed the point of what you're asking.

Pete wrote "i remember that,  but im almost 3 weeks ahead now"  Is there some reason for that?  I consider that advance puzzles are there to help people avoid gaps due to business trips, holidays, going into hospital, work patterns, etc.  I can't see the point in doing them ahead of time just because they are there.  Also it makes it harder to take part in discussions about particular puzzles, which Pete likes to do.

Angel wrote "The key to this puzzle is column 1.

Innie/outie difference on column 1 gives r1c2-r6c1=6"

I did that after I'd spent time looking for simpler steps.  While innies and outies are routinely used for Gentle and Moderate puzzles on this site, I don't expect to need to use innie-outie differences.  That's why I called this puzzle Gentle(?).

Angel:

Once again "Thanks".  No need to apologize for rambling on.  I can't wait to sit down with your second explanation and finally see the light.  I love the Killer puzzles.  They are the only ones I do.  If I learn a new technique from you, it will only lead me to enjoy them more. 

Hi Andrew

I don't submit any puzzles at all now, I only looked at this one because of your original post.

It's a long time since I solved a gentle from this site - but I seem to remember that most needed around 5 minutes, often without any pencil marks. So although not difficult to solve, this one does seem wrongly graded. Or maybe there's another way - perhaps I should have said the 'key for me'...

Actually I love innie/outie differences - sometimes I find I'm using them and ignoring much easier steps.

Jeannette - I agree, killers are my favourite puzzles too.

Angel:

You were right (how often does someone tell you that).  Following your second explanation, I was able to understand the technique you used.  What I wasn't getting at first was the fact that it was a "difference" of 6.  I kept thinking that you meant  the two cells should "equal" six.  Once I entered the 1 and 7, I never had to look for any other innie/outie strategies to solve the puzzle.  I just followed the numbers around to the easiest of solutions. 

Andrew is right too.  I should not have had to use a high level technique in order to easily solve a gentle puzzle.  Without your input, I would still be struggling to solve it using basic skills. 

Walter is right too! Like him, I can't wait to run across another one. 

What a miracle.  Look what shows up on todays killer.

Walter: Check back in tomorrow after the deadline and we'll compare notes as to whether it worked to immediately solve the puzzle like it did for Killer #1395.  I've been reading about the technique and have found out that it only works when a few cells are involved or when the difference between the innie and outies is very large.  Let's hope today's cracks the puzzle. 

Walter - The Innie-Outie Difference on this puzzle didn't work for me either.  Numbers were too low.  I also solved the puzzle "my way" and found it not too difficult.  I will continue to look for opportunities to use the new technique we learned.  That was fun!

Hello Walter, Jeanette and other outies/innies-users. I find this method very useful, and after some testing it's quite easy to find/use, I think. Perhaps you have discovered it already?

Maybe it's obvious to you, but I found one example in killer #1398 (Jan 27th) which is really useful. In nonet 7 there are 3 cells not included in the 9'er, the 15'er and the 4'er. Those 3 cells (G1+G2+J3) must sum up to 17.

We know that G1+G2+F2= 9 and as we just fond out G1+G2+J3 = 17. That means that J3 is 8 greater than F2 amd the only alternatives are 9 and 1. 

I hope it's understandable, keep looking for these outies/innies!

It's understandable but I would probably have more luck finding an x wing or a y wing, neither of which I can find or understand, than finding that clue.  BUT, it is a clue and that's what we're looking for.  Thanks.

Jenete, I found it interesting that the innie/outie  in column 1, a2 and g1, showed a difference of 0 and sure enough, they were equal.  How's your fishing?

Walter:  That is interesting, so is the fact that c9 and j9 are 8 and 1 which is the difference from 38.  You don't ever have to worry about the X-Wing and Y-Wing (there is a Z-wing too) strategies unless you do the other puzzles.   You won't find them in Killers.  Maybe that's why I like them so much.  You don't have to be a Eureka guy to solve them.

It's only 14 degrees in Michigan today.  I only fish in the warm months and I haven't caught anything bigger than the one in my profile.  (They keep getting away from me.) Maybe this summer.

Long John: I'll redo #1398 later this evening and use your Nonet 7 strategy.  I do understand your explanation, I just have to learn how to find these differences by myself.

Hi All.

I am just trying to learn Killer Techniques and find this forum very interesting. I have a problem understanding how you get r5c1=3. I have determined that it can be 3 or 4. What eliminates the 4? Also what does  the reference to outie  r1234 mean?  Thanks to anyone who can explain this to me.

Bert

Hello Bert and welcome to the "killer world". We really enjoy new killer fans, hope you continue solving this wonderful sudokus.

The referende to outies r1234 is based on the fact that each row in a sudoku sums up to 45.

That means that if you add all the sums in these 4 rows included the 14 cage in column 1, you will get the sum 183. As 4 rows sums to 45 x 4 = 180, the extra cell outside the 4 rows (that is the outie r1234) has to be 3.

The opposite is innies. I'll give you the chance to find the c89 innie! Come back if you need more help! regards Torstein

Torstein:

Thanks for the assistance. I couldn't seem to find an explanation anywhere else on this or other web-sites. I did finally finish this puzzle yesterday, but it took a long time. I have a lot to learn it seems. I mainly used regular Sudoku elimination techniques after establishing all the candidates in each cage (a very onerous task). I will have to practice more before entering the competition. And try to find other unique "Killer" strategies. Thanks again.

Bert

Bert

A couple of good sites for learning how to solve killers are http://www.ndorward.com/blog/?page_id=50 (this is the external site referred to on the Daily Killer page and the first killer solving guide I used) and http://www.sudocue.net/killerguide.php (I don't know how long this will be available; it's on a site which is no longer maintained).

I hope this helps you and other would-be killer solvers.

Andrew

Not forgetting:

http://entertainment.timesonline.co.uk/tol/arts_and_entertainment/games_and_puzzles/killer_sudoku/

(which acquainted me with Killers in the first place)

and also killersudokuonline, which will capture huge chunks of your life, if not careful.

Ruud's Assassins did so as well, before he suddenly vanished, but they've been kept alive by addicts at the rcbroughton.co.uk site, if you're truly a glutton...

(In recovery, here..., Griddlers, anyone?, Timesspellingbee?)

s

Hi all..

By following your guidance, I have successfully completed 5 out of six daily "killers". Was too busy one day to finish one, but I have caught the "bug" and find these puzzles very challenging. I doubt that I will seek to make the Honour Roll, but I intend to continue solving for fun. It still takes me and hour or more to finish each one, but I usually watch Hockey, Curling or Super Bowl on TV while solving. So my concentration level is hampered. Anyway, thanks for the advice, enabling me to enjoy a new challenge.  Bert

By the way Pete, what are you smoking?

Hey, Bert!

Friday for 2 weeks - Vancouver. RU ready? I'm referring to the telly)

It might B nice if this forum had something like the Conceptis Puzzles forum has. A PM (private message) button where someone just sends a message to that 1 person, not to the big board.

Jeff