Really stuck on a puzzle

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Really stuck on a puzzle

Postby Raymond035 » Tue Jun 26, 2018 8:26 pm

Kind of new to sudoku. I have tried a lot of advanced techniques I found online. No luck though. Anybody sees a next move?

Image
Raymond035
 
Posts: 1
Joined: 26 June 2018

Re: Really stuck on a puzzle

Postby eleven » Wed Jun 27, 2018 10:35 pm

If i copied it right, this is the grid, where you are:
Code: Select all
+----------------------+----------------------+----------------------+
| 56     7      56     | 2      8      1      | 4      9      3      |
| 1      4      3      | 5      6      9      | 2      8      7      |
| 2      8      9      | 4      3      7      | 16     16     5      |
+----------------------+----------------------+----------------------+
| 569    136    7      | 169    29     26     | 8      13456  146    |
| 4      1369   26     | 169    5      8      | 136    7      126    |
| 8      16     256    | 3      7      4      | 9      1256   126    |
+----------------------+----------------------+----------------------+
| 3      569    4      | 69     1      256    | 7      26     8      |
| 69     2      8      | 7      49     3      | 5      146    1469   |
| 7      56     1      | 8      249    256    | 36     2346   2469   |
+----------------------+----------------------+----------------------+

There are many ways to solve it (and i hope the members will present some).
But do you know x-wings, (hidden) unique rectangles, w-wings and kites ?
Or do you use chains ?
eleven
 
Posts: 1798
Joined: 10 February 2008

Re: Really stuck on a puzzle

Postby Leren » Thu Jun 28, 2018 1:05 am

Code: Select all
*--------------------------------------------------------------------------------*
| 56      7       56       | 2       8       1        | 4       9       3        |
| 1       4       3        | 5       6       9        | 2       8       7        |
| 2       8       9        | 4       3       7        | 16      16      5        |
|--------------------------+--------------------------+--------------------------|
|c569    a136     7        | 16      29      26       | 8      b13456   146      |
| 4      d169-3   26       | 169     5       8        | 136     7       126      |
| 8       16      256      | 3       7       4        | 9       1256    126      |
|--------------------------+--------------------------+--------------------------|
| 3       569     4        | 69      1       256      | 7       26      8        |
| 69      2       8        | 7       49      3        | 5       146     1469     |
| 7       56      1        | 8       249     256      | 36      2346    2469     |
*--------------------------------------------------------------------------------*

Here is a single move that will solve the puzzle and only involves 4 cells. The logic is a bit more involved than we normally get in these sort of enquiries, so I'll talk you through it.

The cells are labelled a-b-c-d. Now suppose cell a was not 3. Now there are only two 3's in Row 4, so cell b would have to be 3. In particular it would not be 5.

Now there are also only two 5's in Row 4, so cell c would have to be 5. In particular it would not be 9. There are only two 9's in Box 4, cells c and d, so cell d would have to be 9.

So let's see where we have gotten with all this. We have shown that if cell a is not 3, cell d must be 9. In particular it is not 3.

On the other hand, if cell a is 3 then cell d is obviously not 3, since it's in the same column or box.

So, if cell a is 3 or is not 3, cell d is not 3. Thus, since cell a can only be 3 or not 3 we can conclude that cell d can't be 3.

In fact, this one elimination solves the whole puzzle, via a cascade of singles.

Leren

PS I just noticed that you have a 9 in r4c4, but not in r4c2 or r9c2.

There is an X Wing of 9's in r57/c24 which makes all three eliminations, so I'm assuming you used this move but just missed the elimination r4c4. In any event it doesn't affect the logic of the move I described above.

Leren
Leren
 
Posts: 3284
Joined: 03 June 2012


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