The New Sudoku Players' Forum

[lovely]

please solve this one, it is killing me. just started learning the game. 3x3. the x are blank cells.

9 X 3 1 X X X X X
5 4 X X X X X X X
6 X X X 9 X X X X
X 9 7 6 X X X 2 X
X X 5 3 X 1 4 X X
X 3 X X X 5 7 8 X
X X X X 8 X X X 7
X X X X X X X 5 6
X X X X X 2 8 X 3

[QBasicMac]

You weren't able to make any placements? I presume you don't use pencilmarks.

OK, Look at cell r4c5. (Row 4 is the 4th from the top, Column 5 is the fifth from the left. We call that r4c5.)

Can a 1 go there? No, because there is already a 1 in r5c6 (same box)
Can a 2 go there? No, because there is already a 2 in r4c8 (same row)
Can a 3 go there? No, because there is already a 3 in r5c4 (same box)
Can a 4 go there? Yes
Can a 5 go there? No, because there is already a 5 in r6c6 (same box)
Can a 6 go there? No, because there is already a 6 in r4c4 (same row)
Can a 7 go there? No, because there is already a 7 in r4c3 (same row)
Can a 8 go there? No, because there is already a 8 in r7c5 (same column)
Can a 9 go there? No, because there is already a 9 in r4c2 (same row)

OK, since only one candidate can go there, you can confidently write a 4 in r4c5.

How did I know to examine that cell? A hunch because of all the numbers in the row, box and column it fell in. I could have been unlucky and found two candidates. But I would keep looking.

Now we have the 4 placed. As a result it turns out that r6c5 has only one legal candidate now: 2. So we place a 2 in r6c5. The notation for that is
r6c5=2

Continuing: r6c4=9, r5c5=7, r4c6=8.

You get the idea. Keep doing that and you will get stuck here

Code: Select all

9-3  1--  ---
54-  ---  ---
6--  -9-  ---

197  648  325
--5  371  469
436  925  781

---  -8-  --7
---  ---  -56
7--  --2  8-3


Well, finally I would notice that there is a 2 and 8 in columns 5 and 6.
So column 4 in the top box (box 2) must have 2 and 8 also, right? Luckily there is already a 1 in r1c4 so we are confident that there is a 2 or 8 in r2c4 and r3c4.

So the other cells in that box must have 123456789-1289=34567, right? But I can't see any benefit of knowing that at this time. I'd say 80% of my hunches go nowhere.

Ok, try looking at the bottom of column c4. It must have 123456789-128639=457

But I see that row 7 already has a 7 at r7c9.
And row 9 has a 7 at r9c1.
That was lucky. That means the 7 in 457 must go in r8c5!
Put it there.

Errk! That is the way I usually solve puzzles, but I also choose easier puzzles than you have. I can't easily see what to do next.

You should learn about pencilmarks to do puzzles like this. If you want, I'm sure someone will post pencilmarks and show some further steps.

Pencilmarks at this point are

Code: Select all

+------------------+-----------------+-----------------+
| 9    278   3     | 1     56   467  | 256   47    248 |
| 5    4     128   | 28    36   367  | 1269  1379  28  |
| 6    1278  128   | 2458  9    347  | 125   1347  248 |
+------------------+-----------------+-----------------+
| 1    9     7     | 6     4    8    | 3     2     5   |
| 28   28    5     | 3     7    1    | 4     6     9   |
| 4    3     6     | 9     2    5    | 7     8     1   |
+------------------+-----------------+-----------------+
| 23   1256  1249  | 45    8    3469 | 129   149   7   |
| 238  128   12489 | 7     13   349  | 129   5     6   |
| 7    156   149   | 45    156  2    | 8     149   3   |
+------------------+-----------------+-----------------+


Mac

[QBasicMac]

Notice that in the last box (Box 9) the only place that a 4 can go is in column 8 since there is already a 4 at r5c7 and since column 9 is full of digits 763. Well, then, 4 in column 8 must therefore go into Box 9.

Great. By studying r1c8, we see it cannot be 931 (row 1) and cannot be 2685 (column 8). That leave 47. But we see that 4 in column 8 must be in box 9. So therefore r1c8=7!!! Place that now.

Now we're getting somewhere. Because r4c3=7 and r0c1=7, then either r3c2 or r1c2 must be 7, right? But we just placed a 7 on row 1. So r3c2=7!!! Place that now.

More progress: look at the 7's on rows 1 and 3 and columns 4 and 5. It forces r2c6=7.

Well, I got stuck again. Bye.

Mac

[Cec]

"You should learn about pencilmarks to do puzzles like this. If you want, I'm sure someone will post pencilmarks and show some further steps..."

Hi lovely and welcome to the Forum,

After applying Mac's above placements your candidate grid will look like this:

Code: Select all

+------------------+-----------------+-----------------+
| 9    28    3     | 1     56   46   | 256   7    248  |
| 5    4     128   | 28    36   367  | 1269  139  28   |
| 6    7     128   | 2458  9    34   | 125   134  248  |
+------------------+-----------------+-----------------+
| 1    9     7     | 6     4    8    | 3     2     5   |
| 28   28    5     | 3     7    1    | 4     6     9   |
| 4    3     6     | 9     2    5    | 7     8     1   |
+------------------+-----------------+-----------------+
| 23   1256  1249  | 45    8    3469 | 129   149   7   |
| 238  128   12489 | 7     13   349  | 129   5     6   |
| 7    156   149   | 45    156  2    | 8     149   3   |
+------------------+-----------------+-----------------+


In column 4 (c4), a "naked pair" [45] enables any other 4's and 5's to be excluded from this column and from Box 8 (one of the nine 3X3 grids)
In r2 there is another "naked pair" [28] which excludes other 2's and 8's in r2. The rest of the puzzle can be solved by looking at each row, column and box to find "naked" or "hidden" singles as the sole candidate in each group (row, column or box) which can then lead to the exclusion of these same candidates from other cels.

The suggested terminology and help in "how to post puzzles" can be found if you click HERE

The following links also show some of the "basic" solving techniques:
http://www.angusj.com/sudoku/hints.php
http://www.sadmansoftware.com/sudoku/techniques.htm

Good luck with your sudoku and "homework".

Cec

edited at 9.30pm simesclara link changed to sadmansoftware. Thanks to Crazy Girl

[lovely]

I was kind of on the right track. I had most of the pencilmarks correct. I just got a lil frustrated. You guys are great.

Thanks a million
Lovely