The New Sudoku Players' Forum

[simleung]

I can solve this by guessing and seeing where it leads me, but that can't be the proper way. I was hoping someone could give me a tip b/c I can't go any further.

Here's the original:

x4x x9x x5x
xxx 3x8 xxx
9x2 xxx 836

xxx 98x xxx
xx8 xxx 6xx
xxx x31 xxx

274 xxx 3x1
xxx 7x2 xxx
x9x x6x x2x

And I got it down to:

843 196 257
xx7 328 xxx
912 5xx 836

xxx 98x xxx
xx8 2xx 6xx
xx9 631 x8x

274 859 361
386 712 xxx
x9x 463 728

But I can't get any further without guessing. Does anyone have a logical next step which would help me solve this the right way?

Thanks.

[rubylips]

First, think about where the 7 goes in Row 6.
Then think about where the 4 goes in Row 6.

[simleung]

I understand your hint about the 7 (thanks) but I'm stupid and I don't get the hint about the 4. As far as I can tell, the 4 in row 6 could go in either column 7 or column 9, and I don't see any of the other 4's (row 2 and row 8) influencing it one way or the other.

Here's another question though, is the following a legitimate problem-solving technique? Can I assume that the 5 must be in r5c6, because otherwise if it's in r4c6, then that means r3c5,6 and r5c5,6 can interchangably contain a 4 or 7, and therefore would result in more than one legitimate solution to the puzzle?

[Nick67]

Here's another question though, is the following a legitimate problem-solving technique? Can I assume that the 5 must be in r5c6, because otherwise if it's in r4c6, then that means r3c5,6 and r5c5,6 can interchangably contain a 4 or 7, and therefore would result in more than one legitimate solution to the puzzle?

Good catch! You are absolutely right. (If you are interested,
the "Standardizing the Uniqueness descriptions..." thread
discusses situations like this in great detail.)

Regarding the 4 in row 6: As you suggested, 4 must go in either
r6c7 or r6c9. That means you can eliminate 4 as a candidate
for the other cells in box 6. (I'm sure that is what rubylips' hint was about.)

Here's another hint, courtesy of Simple Sudoku: check for a naked
pair in row 4. There are 2 cells that have only 2 candidates, and
the 2 candidates are the same. Recognizing that will help you place the 7 in row 4. After that, I think things will get easier.

[teddy]

I can solve this by guessing and seeing where it leads me, but that can't be the proper way. I was hoping someone could give me a tip b/c I can't go any further.

843 196 257
xx7 328 xxx
912 5xx 836

xxx 98x xxx
xx8 2xx 6xx
xx9 631 x8x

274 859 361
386 712 xxx
x9x 463 728

But I can't get any further without guessing. Does anyone have a logical next step which would help me solve this the right way?

Thanks.

edit the row 4,5,6 as below

1456\2356\15---9\8\457 ---145\147\2345
145\35\8 ---2\47\457---6\1479\3459
7\25\9 ---6\3\1 ---45\8\245

Usually I will begin from the easiest space. So try 2 in R6C2 ----then R6C9 is 45-----since R6C7 is also 45 , I get R4C7 is 1----then R4C3 is 5---then R5C2 is 3----then R4C2 is 6----then R4C1 is 1 which is contradict with R4C7=1

I try R6C2= 5 then get the result smoothly.

[Cec]

I can solve this by guessing and seeing where it leads me, but that can't be the proper way. I was hoping someone could give me a tip b/c I can't go any further.

But I can't get any further without guessing. Does anyone have a logical next step which would help me solve this the right way?

Thanks.

I am assuming simleung you want to know whether there are sequential logical steps to solve this puzzle rather than Teddy's above T & E exercise of considering the possible candidates 2 & 5 in r6c2

Yes, it can be solved by applying techniques such as "Locked Candidates 2" and "Naked Pairs" which you can read about here

As mentioned by Nick67 above, 4's are "locked" in r6 (Box6) which enables all other candidate 4's to be excluded from Box6. This leads to a naked pair (15) in r4 which thus excludes the other candidates 1 & 5 from this row. This leaves 7 as the only candidate in r4c8.

By applying normal candidate elimination techniques for rows, columns and boxes, this puzzle can be solved without T & E. If you are still stuck then ask for more help.

Cec