The New Sudoku Players' Forum

[wira]

Hello fellow sudoku lover,

I am currently stuck & need a guidance for solving the next cell.
Would really appreciate your help, thank you.

SUdoku.png (23.02 KiB) Viewed 731 times

[eleven]

Look at the 79's in column 5 and row H. What does it mean for B9 ?
It's a remote pair. (or a kite for 7 and 9).

[wira]

Look at the 79's in column 5 and row H. What does it mean for B9 ?
It's a remote pair. (or a kite for 7 and 9).

Ah remote pair... A new technique I've never heard before.
Thanks a lot eleven!

[eleven]

You are welcome. Thought you wouldn't answer, but then remembered, that the first (3,5?) posts of newbies are blocked for 3 days (though i can't find that in the rules).
So just ask a few more questions

[wira]

Hi eleven,

Yes, I need to wait for the admin approval for every post
Lots of thanks, the remote pair technique helped me solved a couple of expert level sudoku.
And if you don't mind, I need another guidance for the case bellow:


Thanks in advance!!

[Leren]

Code: Select all

*------------------------------------------*
| 3   7    12 | 9 6    5   |*124  8    24  |
| 8   4    5  | 1 23   23  | 6    9    7   |
| 19  29   6  | 7 8    4   |*12   5    3   |
|-------------+------------+---------------|
| 2   6    8  | 5 37   37  | 9    4    1   |
| 7   1    3  | 6 4    9   | 5    2    8   |
| 4   5    9  | 2 1    8   | 37   37   6   |
|-------------+------------+---------------|
| 6   239  7  | 8 259  12  | 234  13   245 |
|c159 239 a12 | 4 2579 6   | 8    137 b25  |
|d5-1 8    4  | 3 257  127 |*27-1 6    9   |
*------------------------------------------*

(1=2) r8c3 - (2=5) r8c9 - r8c1 = (5) r9c1 => - 1 r9c1; stte

Two moves are in the above diagram. The first is in the 3 cells marked *. A pointing pair of 1's in Box 1 removes the 1 from r9c7. That's easy, so I assume you just missed it.

To get further you will need a chain of some sort, or an Alternating Inference Chain in the vernacular. The one I've used is in the cells marked a-b-c-d and I've given you some notation for it, but I'll explain it in words for you.

Suppose r8c3 (Cell a) was not 1. Then it must be 2. So r8c9 (Cell b) would not be 2, so it must be 5. So r8c1 (Cell c) must not be 5. Since there are only two 5's in Column 1, then r9c1 (Cell d) must be 5. In particular it is not 1.

So, if Cell a is not 1, Cell d is not 1. But obviously if Cell a is 1 then Cell d is not 1 since both cells are in the same box. So, whatever value is in Cell a, 1 is not in Cell d. So you can remove 1 from Cell d and the puzzle will solve in singles from there. That's what the stte means in the notation - short for Singles To The End.

You can read about AIC's, for example, here.

Leren

[eleven]

Hi, the most common techniques needed in e.g. harder newspaper puzzles are x-wing and xy-wing. The latter you can find here.

Code: Select all

+--------------------+-------------------+-------------------+
|   3     7     12   | 9     6     5     | 124   8     24    |
|   8     4     5    | 1     23    23    | 6     9     7     |
|   19    29    6    | 7     8     4     | 12    5     3     |
+--------------------+-------------------+-------------------+
|   2     6     8    | 5     37    37    | 9     4     1     |
|   7     1     3    | 6     4     9     | 5     2     8     |
|   4     5     9    | 2     1     8     | 37    37    6     |
+--------------------+-------------------+-------------------+
|   6     239   7    | 8     259   12    | 234   13    245   |
|   59-5  239  #12   | 4     2579  6     | 8     137  P25    |
|  P15    8     4    | 3     257   127   | 27    6     9     |
+--------------------+-------------------+-------------------+

r8c3 (the "pivot") is either 1 or 2. If it is 1, r9c1 is 5. If it is 2, r8c9 is 5 (the 2 cells are called "pincers"). So all cells, which "see" the pincers (r8c123 and r9c789) cannot be 5.

[wira]

Code: Select all

*------------------------------------------*
| 3   7    12 | 9 6    5   |*124  8    24  |
| 8   4    5  | 1 23   23  | 6    9    7   |
| 19  29   6  | 7 8    4   |*12   5    3   |
|-------------+------------+---------------|
| 2   6    8  | 5 37   37  | 9    4    1   |
| 7   1    3  | 6 4    9   | 5    2    8   |
| 4   5    9  | 2 1    8   | 37   37   6   |
|-------------+------------+---------------|
| 6   239  7  | 8 259  12  | 234  13   245 |
|c159 239 a12 | 4 2579 6   | 8    137 b25  |
|d5-1 8    4  | 3 257  127 |*27-1 6    9   |
*------------------------------------------*

(1=2) r8c3 - (2=5) r8c9 - r8c1 = (5) r9c1 => - 1 r9c1; stte

Two moves are in the above diagram. The first is in the 3 cells marked *. A pointing pair of 1's in Box 1 removes the 1 from r9c7. That's easy, so I assume you just missed it.

To get further you will need a chain of some sort, or an Alternating Inference Chain in the vernacular. The one I've used is in the cells marked a-b-c-d and I've given you some notation for it, but I'll explain it in words for you.

Suppose r8c3 (Cell a) was not 1. Then it must be 2. So r8c9 (Cell b) would not be 2, so it must be 5. So r8c1 (Cell c) must not be 5. Since there are only two 5's in Column 1, then r9c1 (Cell d) must be 5. In particular it is not 1.

So, if Cell a is not 1, Cell d is not 1. But obviously if Cell a is 1 then Cell d is not 1 since both cells are in the same box. So, whatever value is in Cell a, 1 is not in Cell d. So you can remove 1 from Cell d and the puzzle will solve in singles from there. That's what the stte means in the notation - short for Singles To The End.

You can read about AIC's, for example, here.

Leren

Hi Leren, thanks for the guidance. I will read about AIC again & again because I haven't understand it.

[wira]

Hi, the most common techniques needed in e.g. harder newspaper puzzles are x-wing and xy-wing. The latter you can find here.

Code: Select all

+--------------------+-------------------+-------------------+
|   3     7     12   | 9     6     5     | 124   8     24    |
|   8     4     5    | 1     23    23    | 6     9     7     |
|   19    29    6    | 7     8     4     | 12    5     3     |
+--------------------+-------------------+-------------------+
|   2     6     8    | 5     37    37    | 9     4     1     |
|   7     1     3    | 6     4     9     | 5     2     8     |
|   4     5     9    | 2     1     8     | 37    37    6     |
+--------------------+-------------------+-------------------+
|   6     239   7    | 8     259   12    | 234   13    245   |
|   59-5  239  #12   | 4     2579  6     | 8     137  P25    |
|  P15    8     4    | 3     257   127   | 27    6     9     |
+--------------------+-------------------+-------------------+

r8c3 (the "pivot") is either 1 or 2. If it is 1, r9c1 is 5. If it is 2, r8c9 is 5 (the 2 cells are called "pincers"). So all cells, which "see" the pincers (r8c123 and r9c789) cannot be 5.

Hi eleven, thanks for the guidance. I already understand x-wing & y-wing, but the xy-wing is giving me a headache
I will try to research about the pincer method that you mention.

[Leren]

Code: Select all

*------------------------------------------*
| 3    7    12 | 9 6    5   | 124 8    24  |
| 8    4    5  | 1 23   23  | 6   9    7   |
| 19   29   6  | 7 8    4   | 12  5    3   |
|--------------+------------+--------------|
| 2    6    8  | 5 37   37  | 9   4    1   |
| 7    1    3  | 6 4    9   | 5   2    8   |
| 4    5    9  | 2 1    8   | 37  37   6   |
|--------------+------------+--------------|
| 6    239  7  | 8 259  12  | 234 13   245 |
| 19-5 239 b12 | 4 2579 6   | 8   137 a25  |
|c15   8    4  | 3 257  127 | 27  6    9   |
*------------------------------------------*

(5=2) r8c9 - (2=1) r8c3 - (1=5) r9c1 => - 5 r8c9; stte

I missed the xy wing, so here it is in words. In cell a, if it is not 5 it is 2. So in cell b it is not 2 so it is 1. So in cell c it is not 1 so it is 5. You can reverse the process, start from cell c, assume it is not 5 and conclude cell a is 5.

This shows that at least one of cells a and c must be 5. So you can remove 5's from the six cells that they can both see, r8c123 and r9c789. There is only one 5 in those cells, so r8c1 is not 5 and the puzzles solves with singles from there.

You can read about xy wings, for example, here.

Leren