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8-3-2006 "Very Hard"

 
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keith



Joined: 19 Sep 2005
Posts: 3178
Location: near Detroit, Michigan, USA

PostPosted: Thu Aug 03, 2006 11:42 pm    Post subject: 8-3-2006 "Very Hard" Reply with quote

There is an X-wing in the starting position. You do not need pencil marks to find it.

OK, I admit the X-wing is not "required" to solve the puzzle, but I had great fun finding it.

Keith
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Marty R.



Joined: 12 Feb 2006
Posts: 5164
Location: Rochester, NY, USA

PostPosted: Fri Aug 04, 2006 4:31 am    Post subject: Reply with quote

Quote:
OK, I admit the X-wing is not "required" to solve the puzzle, but I had great fun finding it.


There wasn't much else required to solve it either, beyond naked sets and locked candidates.
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orly



Joined: 04 Aug 2006
Posts: 1

PostPosted: Fri Aug 04, 2006 8:12 pm    Post subject: Reply with quote

I am here with this puzzle:

Code:

*******************************************************
*     | 89  | 138 *     | 69  | 138 * 36  |     |     *
*  5  |     |     *  7  |     |     *     |  4  |  2  *
*_____________________________________________________*
* 1349| 479 |     *     | 69  | 13  * 36  | 17  |     *
*     |     |  2  *  5  |     |     *     |     |  8  *
*_____________________________________________________*
* 13  | 78  |     *     |     | 138 *     | 17  |     *
*     |     |  6  *  2  |  4  |     *  5  |     |  9  *
*     |     |     *     |     |     *     |     |     *
*******************************************************
* 46  |     |     *     |     | 56  *     |     | 45  *
*     |  1  |  9  *  3  |  7  |     *  8  |  2  |     *
*_____________________________________________________*
*     | 2456| 45  * 46  |     | 256 *     |     |     *
*  7  |     |     *     |  8  |     *  1  |  9  |  3  *
*_____________________________________________________*
* 234 | 2458| 3458* 14  | 125 |     *     |     | 45  *
*     |     |     *     |     |  9  *  7  |  6  |     *
*     |     |     *     |     |     *     |     |     *
*******************************************************
* 149 | 459 | 145 * 89  | 135 |     *     | 358 |     *
*     |     |     *     |     |  7  *  2  |     |  6  *
*_____________________________________________________*
*     | 256 | 15  * 16  | 1235|     *     | 35  |     *
*  8  |     |     *     |     |  4  *  9  |     |  7  *
*_____________________________________________________*
* 269 |     |     * 89  | 25  | 256 *     | 58  |     *
*     |  3  |  7  *     |     |     *  4  |     |  1  *
*     |     |     *     |     |     *     |     |     *
*******************************************************

You both have said that advanced techniques were not needed, but I don't see my next move. Can you please explain what it would be and why?
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David Bryant



Joined: 29 Jul 2005
Posts: 559
Location: Denver, Colorado

PostPosted: Fri Aug 04, 2006 9:18 pm    Post subject: hidden pairs will crack it. Reply with quote

Hi, Orly! Welcome to the forum.

All you need to crack this puzzle is to find a few hidden pairs.

First, look carefully at column 3, and at row 7. You can see the pair {2, 6} already entered in both. Now look at the bottom left 3x3 box (box 7). Because of the way column 3 and row 7 intersect that box, it is evident that the pair {2, 6} must lie in r8c2 & r9c1 ... there are no other cells in which either of those values can possibly be placed.

OK, that was just for warmup. Here's a clue that will get you going again. Smile

Look at the bottom left 3x3 box. The values {3, 8} are already entered there. Then look at row 5, where you will see {3, 8} once again. So there are three cells in column 3 (r5c3, r7c3, and r8c3) that cannot possibly contain either "3" or "8", implying that the hidden pair {3, 8} must lie in r1c3 & r6c3.

(Working from the diagram you posted, you can also spot this by observing the triplet of values {1, 4, 5} in r5c3, r7c3, and r8c3. I think the "hidden pairs" are usually easier to spot without the candidate lists, but either approach works.)

Anyway, with the candidates for r1c3 reduced to {3, 8} you will notice that r1c6 = 1 (unique horizontal), and you should be able to make more progress from there.

Happy sudokuing! dcb
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mazin



Joined: 05 Aug 2006
Posts: 2

PostPosted: Sat Aug 05, 2006 11:35 am    Post subject: Reply with quote

orly wrote:
I am here with this puzzle:

Code:

*******************************************************
*     | 89  | 138 *     | 69  | 138 * 36  |     |     *
*  5  |     |     *  7  |     |     *     |  4  |  2  *
*_____________________________________________________*
* 1349| 479 |     *     | 69  | 13  * 36  | 17  |     *
*     |     |  2  *  5  |     |     *     |     |  8  *
*_____________________________________________________*
* 13  | 78  |     *     |     | 138 *     | 17  |     *
*     |     |  6  *  2  |  4  |     *  5  |     |  9  *
*     |     |     *     |     |     *     |     |     *
*******************************************************
* 46  |     |     *     |     | 56  *     |     | 45  *
*     |  1  |  9  *  3  |  7  |     *  8  |  2  |     *
*_____________________________________________________*
*     | 2456| 45  * 46  |     | 256 *     |     |     *
*  7  |     |     *     |  8  |     *  1  |  9  |  3  *
*_____________________________________________________*
* 234 | 2458| 3458* 14  | 125 |     *     |     | 45  *
*     |     |     *     |     |  9  *  7  |  6  |     *
*     |     |     *     |     |     *     |     |     *
*******************************************************
* 149 | 459 | 145 * 89  | 135 |     *     | 358 |     *
*     |     |     *     |     |  7  *  2  |     |  6  *
*_____________________________________________________*
*     | 256 | 15  * 16  | 1235|     *     | 35  |     *
*  8  |     |     *     |     |  4  *  9  |     |  7  *
*_____________________________________________________*
* 269 |     |     * 89  | 25  | 256 *     | 58  |     *
*     |  3  |  7  *     |     |     *  4  |     |  1  *
*     |     |     *     |     |     *     |     |     *
*******************************************************

You both have said that advanced techniques were not needed, but I don't see my next move. Can you please explain what it would be and why?

Thank you David and Orly.

I was exactly the same point, and stayed up to the early hours last night trying to figure this out.

Hopefully I will remember this method for future use!

I find the jargon a bit confusing, but I realise that is due to my ignorance
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Marty R.



Joined: 12 Feb 2006
Posts: 5164
Location: Rochester, NY, USA

PostPosted: Sat Aug 05, 2006 2:39 pm    Post subject: Reply with quote

Quote:
I find the jargon a bit confusing, but I realise that is due to my ignorance


Mazin, there is a wealth of information available. Just do a search on sudoku or sudoku techniques and you'll find plenty of reading matter which will explain most of the jargon.
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