The New Sudoku Players' Forum

[Aniedunai]

Hello guys I need help solving this one if you could help me I dont know the next move

Code: Select all

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


[jco]

Hello Aniedunai

Look for a place in box 2 for a 7.
Also, look which digits are possible at cells r9c1, r9c2.

[Maxito_Bahiense]

Hi, Aniedunai. The best course of action (unless you have a prodigious visual memory) is to fill in possible candidates for each digit and cell. If you proceed with that, you could build the following grid with pencilmarks:

Code: Select all

.------------------.----------------.--------------------.
| 5689  35689  7   | 4   1358  1268 | 12569  126  123569 |
| 1     35689  345 | 26  358   268  | 24569  246  7      |
| 56    2      345 | 9   135   167  | 1456   8    13456  |
:------------------+----------------+--------------------:
| 56    1      2   | 3   7     4    | 56     9    8      |
| 7     4      9   | 8   6     5    | 12     3    12     |
| 3     56     8   | 1   2     9    | 7      46   456    |
:------------------+----------------+--------------------:
| 4     359    35  | 26  19    126  | 8      7    1269   |
| 2     7      6   | 5   189   18   | 3      14   149    |
| 89    89     1   | 7   4     3    | 269    5    269    |
'------------------'----------------'--------------------'


Following that, there are a couple of easy strategies that you could follow: hidden singles (look where you could fill the remaining digit 7), pointing and claiming (aka locked candidates, which are techniques that here eliminate some candidates for digit 2), naked (locked) pairs (look for example in box 7 how candidates 8 and 9 form a locked pair in the box and in the last row), etc.

[Aniedunai]

I'm very sorry i forgot to put that 7 on the first grid, I have all these candidates but there isn't really any certain number I can put

Code: Select all

89 .  7 | 4  .  .  | 9   2  3
1  .  4 | 26 .  26 | 49  2  7
56 2  4 | 9  .  7  | 4   8  3
------+-------+-----------------
56 1  2 | 3  7  4  | 56  9  8
7  4  9 | 8  6  5  | 12  3  12
3  56 8 | 1  2  9  | 7   4  45
------+-------+-----------------
4  53 53| 26 19 26 | 8   7  19
2  7  6 | 5  89 18 | 3   14 49
89 89 1 | 7  4  3  | 26  5  26


[Hajime]

Two 4's in column 3 ?? Your last puzzle is not very valid anymore. Stick to the plan of Maxito_Bahiense.
The 7 in r3c6 is not even necessary. The last possible cell for a 7 in box2.
The puzzle can be solved with basic methods : Pointing, Claiming and and Naked/Hidden Pairs,Triplets,Quads

[Aniedunai]

Yes in c3 thats where the two possible places the 4 can go along with the other two 4 on c7. The number 7 is already done I had just forgotten to put it before.

[jco]

Yes in c3 thats where the two possible places the 4 can go along with the other two 4 on c7. The number 7 is already done I had just forgotten to put it before.

Code: Select all

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

Still looking at your initial board, the 89 pair at r9c12 implies a 26 pair at r9c79.
Now looking at the givens 2 and 6 at boxes 5,7, we see that at row 7 the only places for 2 and 6 are at r7c46 (as a 26 pair).
That also implies that r2c4 is 2 or 6. These three (26) pair cells (r2c4,r7c46), called my attention
due to a potential UR (unique rectangle), so we must have (8)r2c6.
Now r8c6 has to be 1 and now there is only one place for 8 and 9 at box 8, etc

EDIT: re-phrased the text for clarity (my thanks to Maxito_Bahiense)

[Aniedunai]

Hey, I completed the sudoku after putting 8 on r2c6. It's the first time I've heard about UR(Unique Rectangles) but I can see the logic behind it.
So because of the pair 2 and 6 on r7c6 and also the other one from r2c4 that tells us that the only possibly number on r2c6 is 8 because
if we were to put a 2 on r2c4 and a 6 on r7c6 or vice versa that means the r2c6 cell can't be either a 6 or 2 which leaves only the 8.

[jco]

Hey, I completed the sudoku after putting 8 on r2c6. It's the first time I've heard about UR(Unique Rectangles) but I can see the logic behind it.
So because of the pair 2 and 6 on r7c6 and also the other one from r2c4 that tells us that the only possibly number on r2c6 is 8 because
if we were to put a 2 on r2c4 and a 6 on r7c6 or vice versa that means the r2c6 cell can't be either a 6 or 2 which leaves only the 8.

By the way, one of my favourite threads is this by RW.
It is very inspiring and a nice way to have fun with this way of solving Sudoku puzzles
[sure, it works for puzzles up to a certain level of difficulty like hard].
Anyway, since I often like to revisit that thread (where UR is a valuable tool !) for motivation, it makes sense to mention it.

[Aniedunai]

Thank you very much Jco for your help in this puzzle, I've been able to learn something new again because of it .
I will definitely read the thread by RW, by what I saw he says he solves puzzles without pencilmarks and he explains how that is not as hard as it sounds.
I never done puzzles without pencilmarks expect the easy ones but it does make it much more hard and interesting.