up vote 4 down vote favorite

I keep staring at this sudoku puzzle and can't seem to find the next move.

enter image description here

Is the next move a guessing move? I thought sudoku always has clear solutions, you just need to figure them out.

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  • I think your initial numbers are already wrong.. – Jamal Senjaya Jan 16 at 10:09
  • Can you be more specific? I don't think I've made a mistake. My numbers are written in blue – Adelin Jan 16 at 10:11
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    It might be useful to update your image without the little hint/guess grey numbers, as they are confusing. E.g. the top right set of 9 squares has 2 squares with a little 4, and two with a little 7. Just keep the large black numbers (the starting ones) and the blue ones (your input). – Phylyp Jan 16 at 11:04
  • @Adelin - thank you. I have been able to replay from the start to your current position, except for the 2/7/5 in column 1, and the 5 in column 2. Could you shed some light on how you arrived at those? R6C1 can be 2/5/7, R5C1 can be 2/5, and R7C1 and R6C2 can both be 5/7. – Phylyp Jan 16 at 11:31
  • 5 is for sure in R6C1, dicatated by top middle 3x3 cell. There, you can have 8 and 3 exclusively in the R1 C4 respectively C5, which tells us that the remaining 1 and 5 are on R3, therefore telling us that the 5 in top left 3x3 cell is on C3 which, working togheter with the 5 from R8C6, cuts the bottom left 3x3 in such a way that 5 is only possible in R6C1. The remaining two (7 and 2) are easy – Adelin Jan 16 at 11:42
up vote 5 down vote accepted

No you shouldn't guess. The puzzle has a unique solution. However, you can't continue unless you calculate all possibilities. Once you do that, solving the puzzle will be easy. I have added the possibilities below. If you want to do that on your own, don't look down.

Sudoko possibilities

Once you do that, I think the next step is clear:

Next step

Note:

others pointed out in the comments that it is unclear why that particular cell cannot have a 5. To explain, in the red column there are 2 cells indicated in blue. They have two possibilities: (3,5). No matter how the possibilities are distributed, any of the cells will definitely have a 3 and the other a 5. Which makes it impossible for any other cell in that column to have a 3 or a 5. explanation

Additional explanation (requested by the OP):

Why can't there be a 7 in the last row? Because it can only be in row 7.Explained below: additional explanation

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    How is it clear that in that place it's a 7? Why is it not a 5? – Adelin Jan 16 at 10:53
  • @Adelin if you look at thd possible numbers at that cell, you can see there is only a 7. What makes you think there should be a 5 – Mhmd Jan 16 at 11:00
  • What makes you think there shouldn't be a 5 in that cell? Nothing around it prevents that cell from containing 5. – votbear Jan 16 at 11:03
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    Let us continue this discussion in chat. – Mhmd Jan 16 at 11:49
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    Ah, that clarifies it. Thanks for the explanation. – votbear Jan 17 at 2:05
up vote 0 down vote

For a start:

2,4 and 7 cannot be in the middle square bottom row, which means that there has to be 1 and 6.

This, in turn, means that:

the 8 must be in the top middle and that there must be a 5 to the middle left in the middle square, and so on.

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  • Welcome to Puzzling! This question already had an answer accepted 11 months ago - be sure to read other answers to make sure you aren't duplicating content. – Deusovi♦ Dec 5 at 22:51

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