The New Sudoku Players' Forum

[fredooi]

it's me again....this is from sunday's paper, neither me nor my bro are able to solve it.

Without pencilmarks:

Code: Select all

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

With pencilmarks:

Code: Select all

19    4      6     | 2    13      5   | 8      7      39
29    259    7     | 36   8       4   | 1      359    3569
8     3      15    | 16   7       9   | 2      4      56
-------------------+------------------+-------------------
5     68    239    | 4    29      7   | 369   389     1
7     1     39     | 58   59      6   | 4     2       3589
4     68    29     | 158  1259    3   | 69    589     7
-------------------+------------------+-------------------
129   259   15     | 7    4       8   | 39    6       239
3     7     8      | 9    6       2   | 5     1       4
6     29    4      | 35   35      1   | 7     89      289 

[Pat]

this is from sunday's paper

Code: Select all

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



Code: Select all

19    4      6     | 2    13      5   | 8      7      39
29    259    7     | 36   8       4   | 1      359    3569
8     3      15    | 16   7       9   | 2      4      56
-------------------+------------------+-------------------
5     68    239    | 4    29      7   | 369   389     1
7     1     39     | 58   59      6   | 4     2       3589
4     68    29     | 158  1259    3   | 69    589     7
-------------------+------------------+-------------------
129   259   15     | 7    4       8   | 39    6       239
3     7     8      | 9    6       2   | 5     1       4
6     29    4      | 35   35      1   | 7     89      289 



which newspaper is that?

too tough for me -- needs "forcing chains"

[Carcul]

Code: Select all

 *----------------------------------------------------------*
 | 19    4     6     | 2     13    5     | 8     7     39   |
 | 29    259   7     | 36    8     4     | 1     359   3569 |
 | 8     3     15    | 16    7     9     | 2     4     56   |
 |-------------------+-------------------+------------------|
 | 5     68    239   | 4     29    7     | 369   389   1    |
 | 7     1     39    | 58    59    6     | 4     2     3589 |
 | 4     68    29    | 158   1259  3     | 69    589   7    |
 |-------------------+-------------------+------------------|
 | 129   259   15    | 7     4     8     | 39    6     239  |
 | 3     7     8     | 9     6     2     | 5     1     4    |
 | 6     29    4     | 35    35    1     | 7     89    289  |
 *----------------------------------------------------------*


Let's start by noting that the cell [r6c5] behaves like a bivalue cell (1,5), because of [r6c5]=1(or 5)|=3=[r4c3]-3-[r5c3]=3=[r5c9]-3-[r1c9]=3=
=[r1c5]-3-[r9c5]-5-[r45c5]-2,9-[r6c5]. Therefore we have

[r7c2]=5=[r2c2]-5-[r2c8]=5=[r6c8]-5-[r6c5]-1-[r1c5]=1=[r3c4]-1-
-[r3c3]=1=[r7c3]=5=[r7c2],

and so r7c2=5 which solves the puzzle (together with a trivial BUG).

[fredooi]

hi carcul, i can't understand what you are writing, and i feel that u are not doing any logical deduction in it, can you please explain it further?

well i am from malaysia and this puzzle is from the star newspaper, which is very popular in northern peninsular.

[Luke]

A different approach...

Code: Select all

19    4      6     | 2    13      5   | 8      7      39
29    259    7     | 36   8       4   | 1      359    3569
8     3      15    | 16   7       9   | 2      4      56
-------------------+------------------+-------------------
5     68    *239   | 4    *29     7   | 369   389     1
7     1     39     | 58   59      6   | 4     2       3589
4     68    *29    | 158  *1259   3   | 69    589     7
-------------------+------------------+-------------------
129   259   15     | 7    4       8   | 39    6       239
3     7     8      | 9    6       2   | 5     1       4
6     29    4      | 35   35      1   | 7     89      289

Another x-wing overlay on a Unique Rectangle with diagonal bivalues, like this puzzle from last week. "The diagonal pairs must have the x-wing component," so both r4c5 and r6c3 = 2. This opens up a couple simple wings, then a XY chain or two brings it home.

I'm betting that somehow Glyn will make better use of this UR... <throwing down gauntlet>

[fredooi]

how do u make sure that r4c5 and r6c3 = 2, when it could be r4c3=r6c5=2?

[Jean-Christophe]

Hi,

These are uniqueness techniques.
The x-wing overlay on a Unique Rectangle is AKA Uniqueness Test 6
There two such Uniqueness Test 6 in your puzzle.
At the end, there is BUG+1 (Bivalue Universal Grave)

It can be solved without using uniqueness techniques, but then requires more forcing chains, wings...

[storm_norm]

luke I am going to steal your grid.

this isn't any faster but if you start with a move like the one below then you exploit those {2,9} cells a little differently, as a w-wing.

(9=6)r6c7-(6=8)r6c2-(8)r4c2=(8)r4c8-(8=9)r9c8; means that r7c7 can't be a 9

after you clean up, the grid looks like this

Code: Select all

.------------------.------------------.------------------.
| 19    4     6    | 2     13    5    | 8     7     39   |
| 29    259   7    | 36    8     4    | 1     359   3569 |
| 8     3     15   | 16    7     9    | 2     4     56   |
:------------------+------------------+------------------:
| 5     68   -239  | 4    *29    7    | 69    38    1    |
| 7     1     39   | 58    59    6    | 4     2     358  |
| 4     68   *29   | 158  1-259  3    | 69    58    7    |
:------------------+------------------+------------------:
| 129   259   15   | 7     4     8    | 3     6     29   |
| 3     7     8    | 9     6     2    | 5     1     4    |
| 6     29    4    | 35    35    1    | 7     89    289  |
'------------------'------------------'------------------'

now those {2,9} cells used as a w-wing can eliminate the two's in r4c3 and r6c5...

(2=9)r6c3-(9)r5c3=(9)r5c5-(9=2)r4c5; r4c3 and r6c5 cannot be 2

and then you can go on to use some xy-chains, and whatever else your heart desires, its all in there.

[Luke]

There two such Uniqueness Test 6 in your puzzle.

Could you reveal the other? I missed it.

[fredooi]

thank you guys! now i understand the meaning of uniqueness test. i think i can solve most puzzles that i couldn't previously now.

anyway, i'm still working on this puzzle, to see whether it's really invalid or not...it already takes me some time to understand the theories...

[Pat]

i am from Malaysia
and this puzzle is from the Star newspaper,
which is very popular in northern peninsular

thanks

i'm still working on this puzzle, to see whether it's really invalid or not

just to clarify,
the puzzle is definitely valid,
it has exactly one answer

[Jean-Christophe]

There two such Uniqueness Test 6 in your puzzle.

Could you reveal the other? I missed it.

Here are two WT from my soft JSudoku, with and without uniqueness. Not sure all the wings are required...

Code: Select all

With uniqueness:
Uniqueness Test 6: (29)UR:r46c35 & X-Wing on 2 -> r4c5, r6c3 = 2
XYZ-Wing on 9 with pivot r4c7, pincers r4c3 & r6c7 -> r4c8 <> 9
XY-Wing on 3 with pivot r9c8, pincers r4c8 & r7c7 -> r4c7 <> 3
r7c7 = 3 (hidden single in c7)
r46c7 forms a naked Pair on {69} within n6 -> not elsewhere in n6
W-Wing with strong link on 9 in r1, r2c1 & r7c9 = {29} -> r7c1 <> 2
r2c1 = 2 (hidden single in c1)
XYZ-Wing on 9 with pivot r2c8, pincers r1c9 & r2c2 -> r2c9 <> 9
Uniqueness Test 6: (29)UR:r79c29 & X-Wing on 2 -> r7c9, r9c2 = 2
XY-Chain on 3 with 6 cells (3=9)r1c9-(9=1)r1c1-(1=3)r1c5-(3=5)r9c5-(5=9)r5c5-(9=3)r5c3 -> r5c9<>3
Singles
r2c28 forms a naked Pair on {59} within r2 -> not elsewhere in r2
BUG+1 -> r6c4 = 5

Without uniqueness:
XY-X-Chain on 9|6 with 1 cells 2 links (9=3)r1c9-(3)r1c5=(3)r2c4-(6)r2c4=(6)r2c9 -> r2c9<>9
XY-X-Chain on 8|9 with 2 cells 1 links (8)r4c8=(8)r4c2-(8=6)r6c2-(6=9)r6c7 -> r4c8<>9
XY-Wing on 3 with pivot r9c8, pincers r4c8 & r7c7 -> r4c7 <> 3
r7c7 = 3 (hidden single in c7)
r46c7 forms a naked Pair on {69} within n6 -> not elsewhere in n6
W-Wing with strong link on 9 in r1, r2c1 & r7c9 = {29} -> r7c1 <> 2
r2c1 = 2 (hidden single in c1)
W-Wing with strong link on 9 in r5, r6c3 & r4c5 = {29} -> r4c3, r6c5 <> 2
r6c3 = 2 (hidden single in n4)
r4c5 = 2 (hidden single in n5)
XY-Chain on 3 with 6 cells (3=9)r1c9-(9=1)r1c1-(1=3)r1c5-(3=5)r9c5-(5=9)r5c5-(9=3)r5c3 -> r5c9<>3
Singles
r2c28 forms a naked Pair on {59} within r2 -> not elsewhere in r2
XY-Chain on 5 with 4 cells (5=9)r2c8-(9=3)r1c9-(3=1)r1c5-(1=5)r6c5 -> r6c8<>5
Singles

BTW Selamat datang fredooi

[fredooi]

hi Jean-Christophe! i managed to solve the puzzle using uniqueness method. now trying to work with the non uniqueness method.