The New Sudoku Players' Forum

[hrcjcr]

Anybody have a move that will quickly solve this?

Code: Select all

24    8     247       127       1279      1279    6      3     5       
1     9     6         345       34        35      7      8     2       
257   57    3         267       2678      278     4      9     1       
8     1345  124       1237      1237      6       12     45    9       
27    17    9         8         5         4       3      12    6       
2456  13456 124       9         123       123     8      45    7       
467   146   8         124567    12467     1257    9      26    3       
3     2     17        167       89        89      5      16    4       
9     46    5         12346     12346     123     12     7     8       

[Cec]

Hi hrcjcr,
When requesting help it's a good idea to post both the original puzzle and the stage you have reached. This enables members to see if you have made a mistake. According to Simple Sudoku, the puzzle you have submitted is insoluble. Are you sure you have copied the correct numbers?

Cec

[udosuk]

Cec, it doesn't matter for this one. If you only take the solved cells and leave the pencilmark cells alone, there is a unique valid solution.

So from what I see, the root of the problem is hrcjcr has incorrectly eliminated the 7 from r7c2 and the 1 from r7c8.

So I'll start from this state:

Code: Select all

 *-----------------------------------------------------------------------------*
 | 247     8       247     | 127     1279    1279    | 6       3       5       |
 | 1       9       6       | 345     34      35      | 7       8       2       |
 | 257     57      3       | 267     2678    278     | 4       9       1       |
 |-------------------------+-------------------------+-------------------------|
 | 8       1345    124     | 1237    1237    6       | 12      45      9       |
 | 27      17      9       | 8       5       4       | 3       12      6       |
 | 2456    13456   124     | 9       123     123     | 8       45      7       |
 |-------------------------+-------------------------+-------------------------|
 | 467     1467    8       | 124567  12467   1257    | 9       126     3       |
 | 3       2       17      | 167     89      89      | 5       16      4       |
 | 9       146     5       | 12346   12346   123     | 12      7       8       |
 *-----------------------------------------------------------------------------*

Instead of taking the XYZ-wing for r1c1<>7 and the turbot fish for r9c2<>1, you can find a naked quad in b4 to make some more breakthroughs. It takes some more work to solve it but not too difficult. I'll let you work it out a little bit by yourself first.

[Cec]

Cec, .........It takes some more work to solve it but not too difficult. I'll let you work it out a little bit by yourself first.

Hi udosuk,
It's been a while since I've tackled a sudoku puzzle but after yesterday's thrashing of my beloved Tigers by the Swans and noting hrcjcr's cry for help I thought I'd try my hand at this one. Anyway, I got as far as the following grid after applying "Locked Candidates" and other basic eliminations where Simple Sudoku suggests further eliminations by "Colors" and highlighting cell r9c2 (candidates 1,4,6). This has confused me because I understand "Colors" refers to conjugate cells where only two candidates exist in the cells to be considered by denoting + and - to distinguish their difference to eventually eliminate a candidate which "sees" both a + and - in the same group or unit.

Code: Select all

 *-----------------------------------------------------------------------------*
 | 4       8       27      | 127     1279    1279    | 6       3       5       |
 | 1       9       6       | 345     34      35      | 7       8       2       |
 | 257     57      3       | 267     2678    278     | 4       9       1       |
 |-------------------------+-------------------------+-------------------------|
 | 8       35      124     | 1237    1237    6       | 12      45      9       |
 | 27      17      9       | 8       5       4       | 3       12      6       |
 | 56      356     124     | 9       123     123     | 8       45      7       |
 |-------------------------+-------------------------+-------------------------|
 | 67      1467    8       | 124567  12467   1257    | 9       126     3       |
 | 3       2       17      | 167     89      89      | 5       16      4       |
 | 9       146     5       | 12346   12346   123     | 12      7       8       |
 *-----------------------------------------------------------------------------*


I might add I've also been confused about this puzzle which SS says is insoluble

Cec

[udosuk]

Anyway, I got as far as the following grid after applying "Locked Candidates" and other basic eliminations where Simple Sudoku suggests further eliminations by "Colors" and highlighting cell r9c2 (candidates 1,4,6). This has confused me because I understand "Colors" refers to conjugate cells where only two candidates exist in the cells to be considered by denoting + and - to distinguish their difference to eventually eliminate a candidate which "sees" both a + and - in the same group or unit.

Code: Select all

 *-----------------------------------------------------------------------------*
 | 4       8       27      | 127     1279    1279    | 6       3       5       |
 | 1       9       6       | 345     34      35      | 7       8       2       |
 | 257     57      3       | 267     2678    278     | 4       9       1       |
 |-------------------------+-------------------------+-------------------------|
 | 8       35      124     | 1237    1237    6       |+12      45      9       |
 | 27     +17      9       | 8       5       4       | 3      -12      6       |
 | 56      356     124     | 9       123     123     | 8       45      7       |
 |-------------------------+-------------------------+-------------------------|
 | 67      1467    8       | 124567  12467   1257    | 9       126     3       |
 | 3       2       17      | 167     89      89      | 5       16      4       |
 | 9      *146     5       | 12346   12346   123     |-12      7       8       |
 *-----------------------------------------------------------------------------*

That is a valid "Colors" move. The conjugate cells don't have to contain the same 2 candidates in each of them. The key property is strong links (e.g. bilocational candidates). For this example, r5c28, r5c8+r4c7, r49c7 are all strong links of 1. So we have this conjugate chain:

r5c2:+ => r5c8:- => r4c7:+ => r9c7:-

As a result, r9c2, which sees both r5c2 & r9c7, cannot contain a 1. Other experts will tell you this move is also called a turbot fish.

However, it is not the critical move to solve this puzzle. The critical move is the following:

ALS-xz rule:
A=r5c1={27}
B=r468c3={1247}
x=2
z=7 => r7c1<>7

I might add I've also been confused about this puzzle which SS says is insoluble.

When SS evaluates a puzzle it only checks for the solved cells, and ignores the pencilmarks. That's why when you load the puzzle SS doesn't say anything (implying it's a valid puzzle) before running into trouble when you keep pressing F11 for it to find its own steps. You can type Ctrl-C right after you load the puzzle and type Ctrl-V in Notepad to paste it, you'll get something like this:

Code: Select all

 *-----------*
 |.8.|...|635|
 |196|...|782|
 |..3|...|491|
 |---+---+---|
 |8..|..6|..9|
 |..9|854|3.6|
 |...|9..|8.7|
 |---+---+---|
 |..8|...|9.3|
 |32.|...|5.4|
 |9.5|...|.78|
 *-----------*

 *-----------------------------------------------------------------------------*
 | 24      8       247     | 127     1279    1279    | 6       3       5       |
 | 1       9       6       | 345     34      35      | 7       8       2       |
 | 257     57      3       | 267     2678    278     | 4       9       1       |
 |-------------------------+-------------------------+-------------------------|
 | 8       1345    124     | 1237    1237    6       | 12      45      9       |
 | 27      17      9       | 8       5       4       | 3       12      6       |
 | 2456    13456   124     | 9       123     123     | 8       45      7       |
 |-------------------------+-------------------------+-------------------------|
 | 467     146     8       | 124567  12467   1257    | 9       26      3       |
 | 3       2       17      | 167     89      89      | 5       16      4       |
 | 9       46      5       | 12346   12346   123     | 12      7       8       |
 *-----------------------------------------------------------------------------*

Load the top grid (with clues only) to SS, and you can solve it by yourself no problem (but SS will get stuck).

[ronk]

ALS-xz rule:
A=r5c1={27}
B=r468c3={1247}
x=2
z=7 => r7c1<>7

Nice trick!

[edit: add highlight statements]

[hrcjcr]

Thanks,
All of you.

I know better than to not include the original. Shame on me.

I missed the naked quad altogether. Was too focused on the cells outside of r5c12 in b4.

And a mighty fine mess the missing pencilmark '1' had in r7c8. This led to the other error by incorrect use of a forcing chain in removing the 7 from r7c2.

The naked quad did lead to the solution, but only after multiple chains, wings and reductions.

udosuk,
The ALS you mentioned saved a few moves. Didn't see that initially either.

I may finally have to give up pencil and paper and get a program to keep track of things.

[Cec]

Thanks udosuk for your explanations. Also thanks to ronk for his "nice trick" invisible presentation which I was trying to recall some weeks back as to how this clever trick was done.
Cec