## difficult one

Advanced methods and approaches for solving Sudoku puzzles

### difficult one

Hello,

I am new to the forum so please go easy. I have been working on this one for a few days and am now stuck. Can anyone help me ?

original puzzle:
xxx|xx9|xx1
xxx|1xx|249
x1x|x32|7xx
--------------
8x4|xxx|x7x
xx5|4xx|x8x
2x3|xxx|x1x
--------------
x4x|x16|8xx
xxx|7xx|194
xxx|xx4|xx3

this is how far I got:
x2x|x49|531
xxx|1xx|249
419|532|768
--------------
8x4|2x1|37x
1x5|4x3|982
2x3|xxx|41x
--------------
942|316|857
xxx|72x|194
xxx|xx4|623

any ideas as to the next step ?
monkey

Posts: 13
Joined: 10 August 2005

Have a look at R9C3. Is there a candidate that is unique to the row / column / block?

stuartn
stuartn

Posts: 211
Joined: 18 June 2005

Thanks stuartn.
sorry, had already filled that in. here is the updated status:
x2x|x49|531
xxx|1xx|249
419|532|768
--------------
8x4|2x1|37x
1x5|4x3|982
2x3|xxx|41x
--------------
942|316|857
xxx|72x|194
xx1|xx4|623

still stuck !
monkey

Posts: 13
Joined: 10 August 2005

Make some eliminations of 7's in box 1
Anette

Posts: 55
Joined: 09 June 2005

Okedoke...

Look at the top row - where could the 7's be?

What does that imply for the rest of Box 1? (the top left one)

Subsequently... there are only two places that 3 and 5 can be in Box 1. So that means 3 and 5 must be there, so nothing else can be - so you might as well cross out all other possibilities in those two cells.

Here's the nice bit...because you've got this far, you can look at column 2 and say to yourself "where can the 8's be in this column?" As they can now only be in Box 7 (the bottom left one) you can cross out all other 8's in this box. Which means you now know where a 6 is.

Carry on till complete.

[Ooops, Anette beat me, knew I was saying too much.]
Karyobin

Posts: 396
Joined: 18 June 2005

thanks for the replies Anette and Karyobin,

I am quite new to this so am not sure how to eliminate the 7s in box 1 (I see 5 possibilities)

monkey

Posts: 13
Joined: 10 August 2005

If you look at box 2, the 7 has to be in row 2. Therefore, it can't be in row 2 in box 1.

And then there is only one place left for it in column3.
Anette

Posts: 55
Joined: 09 June 2005

Last edited by hana somekh on Wed Aug 10, 2005 3:53 pm, edited 1 time in total.
hana somekh

Posts: 28
Joined: 30 July 2005

Misprint error in my previous posting

Hi monkey,

In box 2 the digit 7 can only be placed in row 2 of that box.
This is because column 4 already has a 7 in box 8 at column 4 row 8 and therefore cannot be place in row 1 column 4.

Because the box 2 must have the 7's in row 2, ie either in row 2, column 4 or row 2 column 5, therefore, the digit 7 cannot be in column 2 of box 1.

This therefore means that the digit 7 in box 1 can only be in column 1 and column 3, ie row 1 column 1 and row 1 column 3.

Now -- in column 3, the digit 6 and 8 together can only be in row 2 and 8 and therefore can be eliminated from row 1 column 3, and hence leaving a 7 in row 1 column 3.

Hope this helps,
Hana.
hana somekh

Posts: 28
Joined: 30 July 2005

Here's the nice bit...
Karyobin - I wish my maths teacher all those years ago (Bexhill Grammar 69-76) had your style and tact. Marvellous.
stuartn

Posts: 211
Joined: 18 June 2005

Hana, Anette, Karyobin and stuartn,

Thank you - I have seen the light regarding the 7 in box 2. I will see where that leads me and come back with my progress.

I can do blocking fine but haven't a clue regarding wings and fish (must read up).

monkey

Posts: 13
Joined: 10 August 2005

Stay with it. You do not need wings or fish for this particular puzzle, nor for most others you are likely to try. Let me repeat one bit of advice, that was said in different ways by the posters above: When you know a value (7 in your case) must go in a certain group of cells, then it follows that it cannot go in certain other groups of cells. What you concentrate on next is not placing that particular value more exactly, but in making deductions about the remaining values in the other groups of cells. Once you start doing this sort of thing routinely, you are well on your way.
Doyle

Posts: 61
Joined: 11 July 2005

Blummin' well put - 'zackly!

Cheers stuartn. Shame I just left the profession.
Karyobin

Posts: 396
Joined: 18 June 2005

Well, eliminating the 7s from box 1 row 2 was the key that unlocked the whole puzzle.

627|849|531
538|167|249
419|532|768
--------------
894|251|376
165|473|982
273|698|415
--------------
942|316|857
386|725|194
751|984|623

So a big thank you to eveyone who replied for teaching me new stuff.
monkey

Posts: 13
Joined: 10 August 2005

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