## In dire straights (SMH Oct 21)

Post the puzzle or solving technique that's causing you trouble and someone will help

### In dire straights (SMH Oct 21)

Hi to all. I am in dire need of a next move or I will have to give up these puzzles as a lost cause. I have taken a gamble and finished the puzzle but that is not the way to do it. I can not find teh next logical move in the puzzle. If anyone can se it I would be most grateful but please explain the move clearly for me as I am a newcomer. Teh puzzle was No 132 in teh SMH On Oct 21. 68_ 1__ _4_
753 642 981 This is the only way I
4_1 __8 6__
_6_ _81 _54 do it,sorry. I am
__4 2_6 1_8
_1_ _34 _96 %100 sure of it so far
__5 46_ 813
14_ _2_ 567
__6 _15 429 Good luck.
Guest

Posts: 312
Joined: 25 November 2005

There's a naked pair (2 & 5) in block 3, followed by a couple of block/col/row interactions on 9 and 2. Followed by some colouring on 7, then a hidden pair (3 and 7) in row 1, then some block/block interactions on 9, finally an X-Wing of 7s.

Quite an involved puzzle!

S
simes

Posts: 324
Joined: 11 March 2005
Location: UK

Thanks Simes for getting back but I did not understand one word of that. All I really wanted was the next move and why. Still in dire straights. Help. Is there an easy way to explain the next move?
Guest

Posts: 312
Joined: 25 November 2005

Code: Select all
`  *-----------* |68.|1..|.4.| |753|642|981| |4.1|..8|6..| |---+---+---| |.6.|.81|.54| |..4|2.6|1.8| |.1.|.34|.96| |---+---+---| |..5|46.|813| |14.|.2.|567| |..6|.15|429| *-----------*  *-----------------------------------------------------------* | 6     8     29    | 1     579   379   | 237   4     25    | | 7     5     3     | 6     4     2     | 9     8     1     | | 4     29    1     | 3579  579   8     | 6     37    25    | |-------------------+-------------------+-------------------| | 239   6     279   | 79    8     1     | 237   5     4     | | 359   379   4     | 2     579   6     | 1     37    8     | | 258   1     278   | 57    3     4     | 27    9     6     | |-------------------+-------------------+-------------------| | 29    279   5     | 4     6     79    | 8     1     3     | | 1     4     89    | 389   2     39    | 5     6     7     | | 38    37    6     | 378   1     5     | 4     2     9     | *-----------------------------------------------------------*`

There are 2 ways of eliminating the 2 from r1c7:

"locked candidates" - the only place for 2s in box 6 is in column 7, which means a 2 cannot be in that column in box 3.
Or, as simes pointed out, you have a "naked pair" in box 3. Look at the 2 cells that contain 2 and 5 as candidates. One MUST be 2 and the other MUST be 5. So again r1c7 cannot contain a 2.

Again, 3s in box 7 are locked into row 9, so the 3 from r9c4 can be removed as a candidate.

Once you're done with that, check for more locked candidates in box 7

From there, aj's Simple Sudoku uses colors for further elimination - a technique I'm still a beginner with. But I did use an x-wing to eliminate another 7 from box 2.

Actually, a couple more moves down the track and I'm stuck as well. Can you provide the original puzzle, without your additions?
Shazbot

Posts: 220
Joined: 24 September 2005

terry wrote:Thanks Simes for getting back but I did not understand one word of that. All I really wanted was the next move and why. Still in dire straights. Help. Is there an easy way to explain the next move?

There are quite a few eliminations to be made before the next big number can be placed. These eliminations involve various techniques, some of which are not straight-forward. Time to do some reading!

This is the log from my solver for the next step:
Code: Select all
`Note: Cell coordinates are in rYcX format with r1c1 at top-left and r9c9 at bottom-right.Block 3: naked pair 25 in cells r1c9, r3c9 - updating candidates for r1c7Block 7: row 9 must contain 3, removing 3 from candidates for r9c4Block 7: column 2 must contain 7, removing 7 from candidates for r5c2Colouring 7: double exclusion found, eliminating 7 from r1c5, (r5c5 => r5c8 => r3c8 => r1c7)Row 1: hidden pair 37 in cells r1c6, r1c7 - removing other candidates for these cellsBlocks 2 and 5 must contain 9 in columns 4 and 5 - removing 9 from candidates for r8c4X-Wing found at r3c5, r5c5, r3c8, r5c8 for 7 - updating candidates for r3c4r1c6 = 3: forced from either candidate of r3c2`
simes

Posts: 324
Joined: 11 March 2005
Location: UK

shazbot wrote:Actually, a couple more moves down the track and I'm stuck as well.

Yes, this puzzle also requires a "forcing chain" to complete.
It's definitely not a Pappocom puzzle.
angusj

Posts: 306
Joined: 12 June 2005

### original puzzle

For Shazpot the puzzle as it was at the beginning. Have not had a go with your tips yet but will get back to you. Thanks to all for your replys.I;ll be back. 68-1-----
7-3-----1
--1--86--
-6--8--5-
--42-61--
-1--3--9-
--54--8--
1-----5-7
-----5-29
Hope you can reas that. Good look
Guest

Posts: 312
Joined: 25 November 2005

### getting there

Thanks Simes I had a go and folowed it all and understood it all except for..........wait for it.........the last line.(ric6=3 using either candidate from r3c2) Could not work that one out. cant see how the 2 or 9 in that box can get me a solid 3 in r1c6.
Looking forward to hearing back from you,Shazbot or anyone still hanging in there. Cheers again boys. I live in Canberra jsut in case and NO I am not a Polly.
Guest

Posts: 312
Joined: 25 November 2005

I can't find the chain from r3c2 => r1c6 either, Terry, but there's one from r3c2 => r6c1 = 8 which unlocks the puzzle. Hope you can find it without me having to type it all out!

PS: What's a Polly?

PPS : Ok, I looked it up. The curious Australian aversion to word endings! Life's too short for long words?
emm

Posts: 987
Joined: 02 July 2005

Possible chains are:

r3c2=2, r1c3=9, r8c3=8, r8c4=3, r8c6=9, c7c6=7, r1c6=3
or
r3c2=9, r5c2=3, r5c8=7, c3c8=3, r1c7=7, r1c6=3

Simon
Last edited by simes on Tue Oct 25, 2005 5:24 pm, edited 1 time in total.
simes

Posts: 324
Joined: 11 March 2005
Location: UK

Looks so simple when you see it like that (even without the edit!) Now I'm really glad I didn't post my 16 link chain!!
emm

Posts: 987
Joined: 02 July 2005

Thanks to all for their time. I am happy now that I can do any puzzle. teh chains you talk about are only a guessing game. Teh one we talked about to get to r1c6=3 are all IF's. Sure you have to try one No which in this case we put a 2 into r3c2, and it turns out that it had to be a 3 in r1c6. But what if we try a nine in r3c2. WE can still come out with a No for r1c6 being No 7 in this case I think. The fact is it is not till you get further into the puzzle that you find that putting the 9 into row 3 was the wrong move and so it had to be the 2. Hope that is clear. So if in future there is no move to be made I have to take a punt on a No and go with that . If it turns out wrong then it has to be another No. To me this is guessing as there is not a clear move to be made unless you form a CHAIN as you call it and a FEW GUESSES strung together as I see it.
Looking forward to hearing any replies from Simes,Shazbot or anyone on my thoughts. Thanks again, Terry.
Guest

Posts: 312
Joined: 25 November 2005

Terry, here's a reply from anyone.
terry wrote:But what if we try a nine in r3c2. WE can still come out with a No for r1c6 being No 7 in this case I think...

I think not! Did you miss this?
simes wrote: r3c2=2, r1c3=9, r8c3=8, r8c4=3, r8c6=9, c7c6=7, r1c6=3
or
r3c2=9, r5c2=3, r5c8=7, c3c8=3, r1c7=7, r1c6=3

It's funny that you managed to follow all the steps except for the last line –I thought the last line was pretty straightforward once you’d eliminated candidates via all those steps.

terry wrote:teh chains you talk about are only a guessing game

It's trial & error but it's not guessing - if two chains from the same cell lead to the same answer in another cell by different loops then you have a proof, not a guess. It's only guessing if you don't check both loops. simes' chains led to a proof for r1c6. My chains were a lot longer but didn't require the colouring step - they led to a proof for r6c1.

With a valid puzzle you never need to ‘take a punt’ as you put it and you will never be in the position of finding out later in the puzzle that you made a wrong move. Every number you enter is the one and only number for that cell, otherwise you don’t enter it.
emm

Posts: 987
Joined: 02 July 2005

Thanks for that em. I never really checked to see wheather the answer was a 3 or 7. But you are right . If I go either way with a 2 or the 9 ,I get a 3. Meaning it has to be 3. No guessing. Hate to see a longer chain. Think I will need a pencil and rubber next time. Thanks to all again. Terry.
Guest

Posts: 312
Joined: 25 November 2005

Ah! whats a . . . i dunno, but everyone uses scary terms, where as i just say 'box 1' or 'colum 6'. for example, wots a 'naked pair'? plz help!
arcanontis

Posts: 2
Joined: 23 November 2005

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