The New Sudoku Players' Forum

[Leren]

Code: Select all

*-----------*
|6..|.4.|.5.|
|...|8.2|.7.|
|347|...|...|
|---+---+---|
|...|78.|...|
|.1.|4..|..6|
|...|..9|.32|
|---+---+---|
|..9|...|...|
|..1|...|4.7|
|53.|...|...|
*-----------*

[pjb]

Code: Select all

 6       28      28     | 139    4      7      | 139    5      139   
 1       9       5      | 8      36     2      | 36     7      4     
 3       4       7      | 1569   1569   156    | 12689  12689  189   
------------------------+----------------------+---------------------
 29      256     236    | 7      8      1356   |b159    4     b159   
a789     1       3-8    | 4      2      35     |b5789  ab89     6     
 478     5678    468    | 156    156    9      | 1578   3      2     
------------------------+----------------------+---------------------
 2478    2678    9      | 126    16     1468   | 35     1268   35     
 28      268     1      | 23569  3569   568    | 4      2689   7     
 5       3       2468   | 1269   7      1468   | 12689  12689  189   


(8=7)r5c18 - (7=8)r4c79, r5c78 => -8 r5c3; lclste

Phil

[SteveG48]

Code: Select all

 *--------------------------------------------------------------------*
 | 6      28     28     | 139    4      7      | 139    5      139    |
 | 1      9      5      | 8      36     2      | 36     7      4      |
 | 3      4      7      | 1569   1569   156    | 12689  12689  189    |
 *----------------------+----------------------+----------------------|
 | 29     256    236    | 7      8      1356   | 159    4      159    |
 |a789    1      3-8    | 4      2      35     | 5789  a89     6      |
 |b478   b5678  b468    |b156   b156    9      | 1578   3      2      |
 *----------------------+----------------------+----------------------|
 | 2478   2678   9      | 126    16     1468   | 35     1268   35     |
 | 28     268    1      | 23569  3569   568    | 4      2689   7      |
 | 5      3      2468   | 1269   7      1468   | 12689  12689  189    |
 *--------------------------------------------------------------------*


(8=79)r5c18 - (7=14568)r6c12345 => -8 r5c3 ; lclste

[Cenoman]

Code: Select all

 +-----------------------+------------------------+------------------------+
 |  6      28     28     |  139     4      7      |  139     5       139   |
 |  1      9      5      |  8       36     2      |  36      7       4     |
 |  3      4      7      |  1569    1569   156    |  12689   12689   189   |
 +-----------------------+------------------------+------------------------+
 |  29     256    236    |  7       8      1356   |  159     4       159   |
 |  789    1     c38     |  4       2     c35     | a789-5  b89      6     |
 |  478    5678   468    |  156     156    9      | a1578    3       2     |
 +-----------------------+------------------------+------------------------+
 |  2478   2678   9      |  126     16     1468   |  35      1268    35    |
 |  28     268    1      |  23569   3569   568    |  4       2689    7     |
 |  5      3      2468   |  1269    7      1468   |  12689   12689   189   |
 +-----------------------+------------------------+------------------------+

Almost hidden pair: (78)r45c7 = (8)r5c8 - (83=5)r5c36 => -5 r5c7; lclste

[Ngisa]

Code: Select all

+--------------------------+---------------------------+----------------------------+
| 6         28        28   | 139        4         7    |  139        5          139 |
| 1         9         5    | 8          36        2    |  36         7          4   |
| 3         4         7    | 1569       1569      156  |  12689      12689      189 |
+--------------------------+---------------------------+----------------------------+
| 29        256       236  | 7          8         1356 |  159        4          159 |
| 789       1        a38   | 4          2        e5-3  |bd5789      b89         6   |
| 478       5678      468  | 156        156       9    | c1578       3          2   |
+--------------------------+---------------------------+----------------------------+
| 2478      2678      9    | 126        16        1468 |  35         1268       35  |
| 28        268       1    | 23569      3569      3568 |  4          689        7   |
| 5         3         2468 | 1269       7         1468 |  12689      12689      189 |
+--------------------------+---------------------------+----------------------------+


(3=8)r5c3 - r5c78 = (8-7)r6c7 = (7-5)r5c7 = (5)r5c6 => - 3r5c6; lclste

Clement

[eleven]

2 in 1:

Code: Select all

 *-------------------------------------------------------------------------*
 |  6      28     28     |  139     4      7      |  139     5       139   |
 |  1      9      5      |  8       3-6    2      |  36      7       4     |
 |  3      4      7      |  1569    1569   156    |  12689   12689   189   |
 |-----------------------+------------------------+------------------------|
 |  29     256    236    |  7       8      1356   | d159     4      d159   |
 |  789    1    eb3-8    |  4       2    eb35     | e5789   c89      6     |
 |  478    5678   468    |  156    a156    9      |  1578    3       2     |
 |-----------------------+------------------------+------------------------|
 |  2478   2678   9      |  126    a16     1468   |  35      1268    35    |
 |  28     268    1      |  23569   3569   568    |  4       2689    7     |
 |  5      3      2468   |  1269    7      1468   |  12689   12689   189   |
 *-------------------------------------------------------------------------*

(6=5)r67c5 - (5=8)r5c36 - (8=9)r5c8 - (9=5)r4c79 - r5c7 = hp35r5c36 - (5=6)r67c5 => -6r3c5,-8r5c3, stte

[SteveG48]

Wow, Eleven. Well done!

[Leren]

Link to the original puzzle is here. Leren

[eleven]

Wow, Eleven. Well done!

Thanks, Steve. I liked to repeat this (rare) "one-step trick". Though it is of no worth for real solving ...

[SteveG48]

Link to the original puzzle is here. Leren

I've noticed that if you drop a morphed puzzle and the historical puzzle into Hudoku, the solution path is the same in some cases and somewhat different for others. That is, the list of moves all have the same type- XY-wing, pointing pair, etc. On today's, it's different. Any thoughts on what that means with respect to morphed puzzles? Should solutions always morph to valid solutions?

[eleven]

I don't know, how the solution path is programmed in Hudoku. But normally programs make their search top down. So if if it looks for chains and finds more than one with the minimum length, it will keep the first one for the next move. Which one is the first, can change for a morph.

[Leren]

SteveG48 wrote : I've noticed that if you drop a morphed puzzle and the historical puzzle into Hudoku, the solution path is the same in some cases and somewhat different for others.

That will be quite common for morphed puzzles in a computer solver. The reason is that you have to make decisions as to what moves to look at, and what digits to look at, in some order.

So, suppose you had a puzzle that had an X Wing on 1 and a Jellyfish on 4. Well, I think most computer programs would look at moves in the most natural digit order, 1 to 9. So you might find the X Wing first and the Jellyfish second.

Now suppose you morphed the puzzle such that digits 4 and 1 were interchanged. In that case you might find a Jellyfish on 1 first, and that might completely change path of subsequent moves, maybe the X Wing on 4 might not be necessary.

Of course, the final solution must always follow the same morphing steps as the clue set, if the solution is unique. I would have thought that all this was obvious.

Leren

[SteveG48]

Now suppose you morphed the puzzle such that digits 4 and 1 were interchanged. In that case you might find a Jellyfish on 1 first, and that might completely change path of subsequent moves, maybe the X Wing on 4 might not be necessary.

Of course, the final solution must always follow the same morphing steps as the clue set, if the solution is unique. I would have thought that all this was obvious.

Leren

Yes, it does seem rather obvious. However, since Hoduku always searches for particular techniques in a particular order, based on the programmer's opinion of difficulty, it will never find a jellyfish on 1 before an X wing on 4. That's why it was mildly disturbing that the solutions changed. What I didn't take into account is that reversing the order in which 2 X wings, for example, was found could change the whole complexion of things. Senior moment.

[Leren]

Hi Steve, if you look here you'll find a rather odd case (to me at least) of a contributor who had played a UR but needed help with a naked pair. Now that's what I'd call a .... courageous .... solving path .

Leren

[eleven]

Well, HappieHappy had pencilmarks in his grid.

But without them the UR is far easier to spot than the naked pair.
Here you immediately see, that 19 is left for the # cells, therefore can be eliminated from X (r7c6).

Code: Select all

 +-------+-------+-------+
 | 3 6 1 | . . . | 2 . . |
 | 9 4 8 | 1 2 3 | 7 5 6 |
 | 7 5 2 | . . 6 | 1 3 . |
 +-------+-------+-------+
 | . 2 5 | 9 3 8 | . . . |
 | 8 3 6 | . . . | 9 . 2 |
 | . 7 9 | 2 6 . | 5 8 3 |
 +-------+-------+-------+
 | 2 # 3 | 6 . X | 8 . . |
 | 5 8 7 | 3 . 2 | . . 1 |
 | 6 # 4 | 7 8 # | 3 2 5 |
 +-------+-------+-------+

But how would you see the naked pair ? For the cells in c5 3-5 candidates are left both in the row and the box.
You either would have to count them out, or see the hidden triple 157, which definitely is harder.

Code: Select all

 +-------+-------+-------+
 | 3 6 1 | . T . | 2 . . |
 | 9 4 8 | 1 2 3 | 7 5 6 |
 |*7*5 2 | . X 6 |*1 3 . |
 +-------+-------+-------+
 | . 2 5 | 9 3 8 | . . . |
 | 8 3 6 | . T . | 9 . 2 |
 | . 7 9 | 2 6 . | 5 8 3 |
 +-------+-------+-------+
 | 2 . 3 | 6 T . | 8 . . |
 |*5 8*7 | 3 X 2 | . .*1 |
 | 6 . 4 | 7 8 . | 3 2 5 |
 +-------+-------+-------+

After the UR: If you know, that the puzzle creator likes xy-wings, you might start to look at other 2-digit cells there - and find the xy-wing (you already knew 14 and 19).

Code: Select all

 +-------+-------+-------+
 | 3 6 1 | . . . | 2 . . |
 | 9 4 8 | 1 2 3 | 7 5 6 |
 | 7 5 2 | . . 6 | 1 3 . |
 +-------+-------+-------+
 | . 2 5 | 9 3 8 | . . . |
 | 8 3 6 | . . . | 9 . 2 |
 | . 7 9 | 2 6 14| 5 8 3 |
 +-------+-------+-------+
 | 2 . 3 | 6 . 45| 8 . . |
 | 5 8 7 | 3 49 2| . . 1 |
 | 6 . 4 | 7 8 19| 3 2 5 |
 +-------+-------+-------+

And the puzzle is quickly solved without finding the naked pair.