Sudoku aid, please

Cafe Society
1

I recently started doing sudoku (for on the train.) I did two “easy” ones pretty easy, so I switched to the “advanced” book and am now on #4 in the book. But I am at a dead end. I’ve verified the squares I have filled versus the answer section (ignoring the squares I don’t have), and they are all correct. So I suspect that there is some method to determine a box that I haven’t yet deduced in my long history of five solved puzzles.

The original box was:


- 8 - | - - 5 | - - -
1 - - | - 2 - | - 6 -
- - - | 1 - - | 4 - - 

- - 7 | - - 8 | - - 5
- 9 - | - 4 - | - 3 -
4 - - | 3 - - | 7 - -

- - 1 | - - 2 | - - -
- 7 - | - 5 - | - - 8
- - - | 9 - - | - 5 -

Now refering to the boxes by coordinates (A -> I from left to right, and 1 -> 9 from top to bottom), I have solved…

[spoiler]C3 = 5
D2 = 8
G2 = 5
H3 = 8

A4 = 3
B4 = 1
B6 = 5
C6 = 8
D4 = 2
D5 = 5
F5 = 7
H4 = 4
G5 = 8
I5 = 1

A7 = 5
A9 = 8
E7 = 8[/spoiler]

And…resorting to brute forcing, I currently have the following listed as possibilities for each of the remaining squares…

[spoiler]A1 = 2,6,7,9
C1 = 2,3,4,6,9
B2 = 3,4
C2 = 3,4,9
A3 = 2,6,7,9
B3 = 2,3,6

D1 = 4,6,7
E1 = 3,6,7,9
F2 = 3,4,9
E3 = 3,6,7,9
F3 = 3,6,9

G1 = 1,2,3,9
H1 = 1,2,7,9
I1 = 2,3,7,9
I2 = 3,7,9
I3 = 2,3,7,9

A5 = 2,6
C5 = 2,6

E4 = 6,9
E6 = 1,6,9
F6 = 1,6,9

G4 = 6,9
H6 = 2,9
I6 = 2,6,9

B7 = 3,4,6
A8 = 2,6,9
C8 = 2,3,4,6,9
B9 = 2,3,4,6
C9 = 2,3,4,6

D7 = 4,6,7
D8 = 4,6
F8 = 1,3,4,6
E9 = 1,3,6,7
F9 = 1,3,4,6

G7 = 3,6,9
H7 = 7,9
I7 = 3,4,6,7,9
G8 = 1,2,3,6
H8 = 1,2
G9 = 1,2,3,6
I9 = 2,3,4,6,7
[/spoiler]
(hopefully, I typed that all in correctly)

But running combinations within a 3X3 box I’m not having any luck with finding anything being ruled out for a position. And running combos between multiple boxes seems rather extreme, regardless of whether it is an “advanced” book or not.

I suspect that there is some pattern that I just haven’t yet learned to look for, so do any of you experienced folk out there see where the weak point is in this puzzle?

  • Given that a sudoku is computer generated and that the book is Japanese, I am doubting that this is any sort of copywrite violation. But otherwise…well apologies.
2

I’m not even gonna look at this exact puzzle – just say that doing pretty well on two easy ones isn’t enough to get you to the advanced stage. There’s a slew of little tricks you’ll learn as you go along. Get a book with easy, medium, hard, do all the easy, do all the medium, and see how you do on the hard then.

3

http://angusj.com/sudoku/ has tips on solving puzzles and a helpful puzzle maker/solver.

4

Very nice. The strategy page has some nice info.

5

Well, the next number that is definite is a 7 at I2. The reasoning behind this is as follows:

Since you already have a 7 at B8, and one at C4, the 7 in the first column has to go to A1 or A3. If you put it A3: the second set of nine in the first row can only have the 7 at D1 or E1. that leaves only I2 for the third 7 in the first row of sets.

If you place the 7 at A1, the second set of nine can only have the 7 at E3, so that again leaves only I2 for the 7.

So, you can be sure that I2 = 7. I’ll try to go on from there if you need further help.

6

Actually, a simpler explanation is as follows. You need a 7 in row 2. You can’t put it at B2 (due to the 7 at B8), you can’t put it at C2 (due to the 7 at C4), and you can’t put it at F2 (due to the 7 at F5). that only leaves I2 for the 7. Is that a little clearer?

7

I’ve been beaten to the punch by total blank but since it took me a while to construct this post, here it is.

I think you have a couple of errors. G8 should be 1,2,3,6,9 and H8 should be 1,2,9.

This doesn’t immediately help you.

However, looking at row 2, I2 is a 7. It is the only possible 7 on that row. Erase the other 7’s in the top right box and in column I.

Now look at the bottom right box. The 7 must be in H7. Erase the 7 in D7 which gives you 4,6 in D7 and D8. Erase the other 4’s and 6’s in the bottom middle box. You can see that E9 must contain a 7.

Still in the bottom middle box you have 1,3 in both F8 and F9. You can now erase the other 1’s and 3’s in column F.

Carry on from there.

8

I’ll need to look at the puzzle again to check your two’s findings, but I do remember G8 and H8 and neither can have a nine. A8 and C8 are the only possibilities for a nine in the bottom-left box, so regardless of which it is, row eight can’t have a nine in the bottom right box.

9

And thank you all. I’ll study all this to see where my brain failed me (and of course if necessary recceed to easier puzzles.) But no more hints please. :slight_smile:

10

My mistake.

G8 and H8 cannot contain a 9.