How do I solve this sudoku without guessing?












2












$begingroup$


I have filled all the possible singles. Also identified and shortlisted candidates, pointing pairs. How do I move ahead without guessing?



enter image description here



PS: I applied "Nishio", choosing one of the two possible candidate values on row 1, column 1. 7 will come in top left. Using which I can solve the rest of the puzzle. But it is "guessing". Any other way?










share|improve this question









$endgroup$












  • $begingroup$
    Not sure if any of the advanced techniques to reduce the candidates here can be applied somewhere? I will also take a look if I can apply any of them.
    $endgroup$
    – Kevin Cruijssen
    Dec 10 '18 at 17:07
















2












$begingroup$


I have filled all the possible singles. Also identified and shortlisted candidates, pointing pairs. How do I move ahead without guessing?



enter image description here



PS: I applied "Nishio", choosing one of the two possible candidate values on row 1, column 1. 7 will come in top left. Using which I can solve the rest of the puzzle. But it is "guessing". Any other way?










share|improve this question









$endgroup$












  • $begingroup$
    Not sure if any of the advanced techniques to reduce the candidates here can be applied somewhere? I will also take a look if I can apply any of them.
    $endgroup$
    – Kevin Cruijssen
    Dec 10 '18 at 17:07














2












2








2





$begingroup$


I have filled all the possible singles. Also identified and shortlisted candidates, pointing pairs. How do I move ahead without guessing?



enter image description here



PS: I applied "Nishio", choosing one of the two possible candidate values on row 1, column 1. 7 will come in top left. Using which I can solve the rest of the puzzle. But it is "guessing". Any other way?










share|improve this question









$endgroup$




I have filled all the possible singles. Also identified and shortlisted candidates, pointing pairs. How do I move ahead without guessing?



enter image description here



PS: I applied "Nishio", choosing one of the two possible candidate values on row 1, column 1. 7 will come in top left. Using which I can solve the rest of the puzzle. But it is "guessing". Any other way?







sudoku






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Dec 10 '18 at 16:57









jerrymousejerrymouse

1112




1112












  • $begingroup$
    Not sure if any of the advanced techniques to reduce the candidates here can be applied somewhere? I will also take a look if I can apply any of them.
    $endgroup$
    – Kevin Cruijssen
    Dec 10 '18 at 17:07


















  • $begingroup$
    Not sure if any of the advanced techniques to reduce the candidates here can be applied somewhere? I will also take a look if I can apply any of them.
    $endgroup$
    – Kevin Cruijssen
    Dec 10 '18 at 17:07
















$begingroup$
Not sure if any of the advanced techniques to reduce the candidates here can be applied somewhere? I will also take a look if I can apply any of them.
$endgroup$
– Kevin Cruijssen
Dec 10 '18 at 17:07




$begingroup$
Not sure if any of the advanced techniques to reduce the candidates here can be applied somewhere? I will also take a look if I can apply any of them.
$endgroup$
– Kevin Cruijssen
Dec 10 '18 at 17:07










3 Answers
3






active

oldest

votes


















3












$begingroup$

You can spot that




the 1, 7 cell cannot be a 4 (and therefore is an 8)




because




setting it to 4 forces an 8 into cell 5,7; which forces a 4 into cell 5,3; which eliminates 4 as a possibility from all of the remaining open cells in the top left block (cells 1,2 and 3,3).







share|improve this answer









$endgroup$





















    2












    $begingroup$

    You could spot that:




    In the top left block, the bottom right 4/6 cell must be a 6.




    Why?




    Because if it is a 4 then in the bottom left block the right side becomes 5/6,5/6. But now the solution isn't unique as setting either of these cells as 5 has no vertical effect on the board (from the bottom right block).







    share|improve this answer









    $endgroup$













    • $begingroup$
      I am still unclear. What is the vertical effect in bottom right block please?
      $endgroup$
      – jerrymouse
      Dec 10 '18 at 19:00










    • $begingroup$
      I'm confused. Using (column,row) notation: setting (3,3) to 4 would require (1,7) to be 4, then (2,9) to be 8, (9,9) to be 5, (3,9) would be 6, and (3,8) would be 5. No ambiguity.
      $endgroup$
      – user3294068
      Dec 10 '18 at 19:31










    • $begingroup$
      @user3294068; well it can't be a 4 according to OP's p.s.
      $endgroup$
      – JonMark Perry
      Dec 10 '18 at 19:49










    • $begingroup$
      @jerrymouse; if you follow my logic, we could have both 568:645 or 645:568 equally, which bears no impact on the rest of the grid.
      $endgroup$
      – JonMark Perry
      Dec 10 '18 at 19:51






    • 1




      $begingroup$
      I might prefer guessing (brute force all options, doesn't seem too difficult here) to this approach, though: if you base any deductions on the solution's assumed uniqueness, you can only reach "an answer" at best. If you want to reach "the answer", you can't assume uniqueness, you have to prove it instead.
      $endgroup$
      – Bass
      Dec 10 '18 at 20:54



















    1












    $begingroup$

    You can notice




    r2c1, r7c1, r3c5, r7c5 form a finned X-Wing for 4.




    Thus




    Consider r2c1. It must be either 4 or 8. If r2c1 is 4 that forces r3c3 to be 6. If r2c1 is 8 that forces r7c1 to be 4 which forces r7c5 to be 8 which forces r3c5 to be 4 which forces r3c3 to be 6. So if r2c1 is either 4 or 8 r3c3 is forced to be 6.




    Hopefully you can get it from there.






    share|improve this answer










    New contributor




    Rocus Halbasch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
    Check out our Code of Conduct.






    $endgroup$













    • $begingroup$
      Hi Rocus, welcome to PSE. Please hide your answers using ">!"
      $endgroup$
      – Greg
      13 hours ago










    • $begingroup$
      Yeah. Just figured out how that works. This was my first answer.
      $endgroup$
      – Rocus Halbasch
      13 hours ago










    • $begingroup$
      No problem. Happy puzzling!
      $endgroup$
      – Greg
      13 hours ago











    Your Answer





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    3 Answers
    3






    active

    oldest

    votes








    3 Answers
    3






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    3












    $begingroup$

    You can spot that




    the 1, 7 cell cannot be a 4 (and therefore is an 8)




    because




    setting it to 4 forces an 8 into cell 5,7; which forces a 4 into cell 5,3; which eliminates 4 as a possibility from all of the remaining open cells in the top left block (cells 1,2 and 3,3).







    share|improve this answer









    $endgroup$


















      3












      $begingroup$

      You can spot that




      the 1, 7 cell cannot be a 4 (and therefore is an 8)




      because




      setting it to 4 forces an 8 into cell 5,7; which forces a 4 into cell 5,3; which eliminates 4 as a possibility from all of the remaining open cells in the top left block (cells 1,2 and 3,3).







      share|improve this answer









      $endgroup$
















        3












        3








        3





        $begingroup$

        You can spot that




        the 1, 7 cell cannot be a 4 (and therefore is an 8)




        because




        setting it to 4 forces an 8 into cell 5,7; which forces a 4 into cell 5,3; which eliminates 4 as a possibility from all of the remaining open cells in the top left block (cells 1,2 and 3,3).







        share|improve this answer









        $endgroup$



        You can spot that




        the 1, 7 cell cannot be a 4 (and therefore is an 8)




        because




        setting it to 4 forces an 8 into cell 5,7; which forces a 4 into cell 5,3; which eliminates 4 as a possibility from all of the remaining open cells in the top left block (cells 1,2 and 3,3).








        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Dec 11 '18 at 15:23









        HellionHellion

        1,901819




        1,901819























            2












            $begingroup$

            You could spot that:




            In the top left block, the bottom right 4/6 cell must be a 6.




            Why?




            Because if it is a 4 then in the bottom left block the right side becomes 5/6,5/6. But now the solution isn't unique as setting either of these cells as 5 has no vertical effect on the board (from the bottom right block).







            share|improve this answer









            $endgroup$













            • $begingroup$
              I am still unclear. What is the vertical effect in bottom right block please?
              $endgroup$
              – jerrymouse
              Dec 10 '18 at 19:00










            • $begingroup$
              I'm confused. Using (column,row) notation: setting (3,3) to 4 would require (1,7) to be 4, then (2,9) to be 8, (9,9) to be 5, (3,9) would be 6, and (3,8) would be 5. No ambiguity.
              $endgroup$
              – user3294068
              Dec 10 '18 at 19:31










            • $begingroup$
              @user3294068; well it can't be a 4 according to OP's p.s.
              $endgroup$
              – JonMark Perry
              Dec 10 '18 at 19:49










            • $begingroup$
              @jerrymouse; if you follow my logic, we could have both 568:645 or 645:568 equally, which bears no impact on the rest of the grid.
              $endgroup$
              – JonMark Perry
              Dec 10 '18 at 19:51






            • 1




              $begingroup$
              I might prefer guessing (brute force all options, doesn't seem too difficult here) to this approach, though: if you base any deductions on the solution's assumed uniqueness, you can only reach "an answer" at best. If you want to reach "the answer", you can't assume uniqueness, you have to prove it instead.
              $endgroup$
              – Bass
              Dec 10 '18 at 20:54
















            2












            $begingroup$

            You could spot that:




            In the top left block, the bottom right 4/6 cell must be a 6.




            Why?




            Because if it is a 4 then in the bottom left block the right side becomes 5/6,5/6. But now the solution isn't unique as setting either of these cells as 5 has no vertical effect on the board (from the bottom right block).







            share|improve this answer









            $endgroup$













            • $begingroup$
              I am still unclear. What is the vertical effect in bottom right block please?
              $endgroup$
              – jerrymouse
              Dec 10 '18 at 19:00










            • $begingroup$
              I'm confused. Using (column,row) notation: setting (3,3) to 4 would require (1,7) to be 4, then (2,9) to be 8, (9,9) to be 5, (3,9) would be 6, and (3,8) would be 5. No ambiguity.
              $endgroup$
              – user3294068
              Dec 10 '18 at 19:31










            • $begingroup$
              @user3294068; well it can't be a 4 according to OP's p.s.
              $endgroup$
              – JonMark Perry
              Dec 10 '18 at 19:49










            • $begingroup$
              @jerrymouse; if you follow my logic, we could have both 568:645 or 645:568 equally, which bears no impact on the rest of the grid.
              $endgroup$
              – JonMark Perry
              Dec 10 '18 at 19:51






            • 1




              $begingroup$
              I might prefer guessing (brute force all options, doesn't seem too difficult here) to this approach, though: if you base any deductions on the solution's assumed uniqueness, you can only reach "an answer" at best. If you want to reach "the answer", you can't assume uniqueness, you have to prove it instead.
              $endgroup$
              – Bass
              Dec 10 '18 at 20:54














            2












            2








            2





            $begingroup$

            You could spot that:




            In the top left block, the bottom right 4/6 cell must be a 6.




            Why?




            Because if it is a 4 then in the bottom left block the right side becomes 5/6,5/6. But now the solution isn't unique as setting either of these cells as 5 has no vertical effect on the board (from the bottom right block).







            share|improve this answer









            $endgroup$



            You could spot that:




            In the top left block, the bottom right 4/6 cell must be a 6.




            Why?




            Because if it is a 4 then in the bottom left block the right side becomes 5/6,5/6. But now the solution isn't unique as setting either of these cells as 5 has no vertical effect on the board (from the bottom right block).








            share|improve this answer












            share|improve this answer



            share|improve this answer










            answered Dec 10 '18 at 17:49









            JonMark PerryJonMark Perry

            18k63786




            18k63786












            • $begingroup$
              I am still unclear. What is the vertical effect in bottom right block please?
              $endgroup$
              – jerrymouse
              Dec 10 '18 at 19:00










            • $begingroup$
              I'm confused. Using (column,row) notation: setting (3,3) to 4 would require (1,7) to be 4, then (2,9) to be 8, (9,9) to be 5, (3,9) would be 6, and (3,8) would be 5. No ambiguity.
              $endgroup$
              – user3294068
              Dec 10 '18 at 19:31










            • $begingroup$
              @user3294068; well it can't be a 4 according to OP's p.s.
              $endgroup$
              – JonMark Perry
              Dec 10 '18 at 19:49










            • $begingroup$
              @jerrymouse; if you follow my logic, we could have both 568:645 or 645:568 equally, which bears no impact on the rest of the grid.
              $endgroup$
              – JonMark Perry
              Dec 10 '18 at 19:51






            • 1




              $begingroup$
              I might prefer guessing (brute force all options, doesn't seem too difficult here) to this approach, though: if you base any deductions on the solution's assumed uniqueness, you can only reach "an answer" at best. If you want to reach "the answer", you can't assume uniqueness, you have to prove it instead.
              $endgroup$
              – Bass
              Dec 10 '18 at 20:54


















            • $begingroup$
              I am still unclear. What is the vertical effect in bottom right block please?
              $endgroup$
              – jerrymouse
              Dec 10 '18 at 19:00










            • $begingroup$
              I'm confused. Using (column,row) notation: setting (3,3) to 4 would require (1,7) to be 4, then (2,9) to be 8, (9,9) to be 5, (3,9) would be 6, and (3,8) would be 5. No ambiguity.
              $endgroup$
              – user3294068
              Dec 10 '18 at 19:31










            • $begingroup$
              @user3294068; well it can't be a 4 according to OP's p.s.
              $endgroup$
              – JonMark Perry
              Dec 10 '18 at 19:49










            • $begingroup$
              @jerrymouse; if you follow my logic, we could have both 568:645 or 645:568 equally, which bears no impact on the rest of the grid.
              $endgroup$
              – JonMark Perry
              Dec 10 '18 at 19:51






            • 1




              $begingroup$
              I might prefer guessing (brute force all options, doesn't seem too difficult here) to this approach, though: if you base any deductions on the solution's assumed uniqueness, you can only reach "an answer" at best. If you want to reach "the answer", you can't assume uniqueness, you have to prove it instead.
              $endgroup$
              – Bass
              Dec 10 '18 at 20:54
















            $begingroup$
            I am still unclear. What is the vertical effect in bottom right block please?
            $endgroup$
            – jerrymouse
            Dec 10 '18 at 19:00




            $begingroup$
            I am still unclear. What is the vertical effect in bottom right block please?
            $endgroup$
            – jerrymouse
            Dec 10 '18 at 19:00












            $begingroup$
            I'm confused. Using (column,row) notation: setting (3,3) to 4 would require (1,7) to be 4, then (2,9) to be 8, (9,9) to be 5, (3,9) would be 6, and (3,8) would be 5. No ambiguity.
            $endgroup$
            – user3294068
            Dec 10 '18 at 19:31




            $begingroup$
            I'm confused. Using (column,row) notation: setting (3,3) to 4 would require (1,7) to be 4, then (2,9) to be 8, (9,9) to be 5, (3,9) would be 6, and (3,8) would be 5. No ambiguity.
            $endgroup$
            – user3294068
            Dec 10 '18 at 19:31












            $begingroup$
            @user3294068; well it can't be a 4 according to OP's p.s.
            $endgroup$
            – JonMark Perry
            Dec 10 '18 at 19:49




            $begingroup$
            @user3294068; well it can't be a 4 according to OP's p.s.
            $endgroup$
            – JonMark Perry
            Dec 10 '18 at 19:49












            $begingroup$
            @jerrymouse; if you follow my logic, we could have both 568:645 or 645:568 equally, which bears no impact on the rest of the grid.
            $endgroup$
            – JonMark Perry
            Dec 10 '18 at 19:51




            $begingroup$
            @jerrymouse; if you follow my logic, we could have both 568:645 or 645:568 equally, which bears no impact on the rest of the grid.
            $endgroup$
            – JonMark Perry
            Dec 10 '18 at 19:51




            1




            1




            $begingroup$
            I might prefer guessing (brute force all options, doesn't seem too difficult here) to this approach, though: if you base any deductions on the solution's assumed uniqueness, you can only reach "an answer" at best. If you want to reach "the answer", you can't assume uniqueness, you have to prove it instead.
            $endgroup$
            – Bass
            Dec 10 '18 at 20:54




            $begingroup$
            I might prefer guessing (brute force all options, doesn't seem too difficult here) to this approach, though: if you base any deductions on the solution's assumed uniqueness, you can only reach "an answer" at best. If you want to reach "the answer", you can't assume uniqueness, you have to prove it instead.
            $endgroup$
            – Bass
            Dec 10 '18 at 20:54











            1












            $begingroup$

            You can notice




            r2c1, r7c1, r3c5, r7c5 form a finned X-Wing for 4.




            Thus




            Consider r2c1. It must be either 4 or 8. If r2c1 is 4 that forces r3c3 to be 6. If r2c1 is 8 that forces r7c1 to be 4 which forces r7c5 to be 8 which forces r3c5 to be 4 which forces r3c3 to be 6. So if r2c1 is either 4 or 8 r3c3 is forced to be 6.




            Hopefully you can get it from there.






            share|improve this answer










            New contributor




            Rocus Halbasch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
            Check out our Code of Conduct.






            $endgroup$













            • $begingroup$
              Hi Rocus, welcome to PSE. Please hide your answers using ">!"
              $endgroup$
              – Greg
              13 hours ago










            • $begingroup$
              Yeah. Just figured out how that works. This was my first answer.
              $endgroup$
              – Rocus Halbasch
              13 hours ago










            • $begingroup$
              No problem. Happy puzzling!
              $endgroup$
              – Greg
              13 hours ago
















            1












            $begingroup$

            You can notice




            r2c1, r7c1, r3c5, r7c5 form a finned X-Wing for 4.




            Thus




            Consider r2c1. It must be either 4 or 8. If r2c1 is 4 that forces r3c3 to be 6. If r2c1 is 8 that forces r7c1 to be 4 which forces r7c5 to be 8 which forces r3c5 to be 4 which forces r3c3 to be 6. So if r2c1 is either 4 or 8 r3c3 is forced to be 6.




            Hopefully you can get it from there.






            share|improve this answer










            New contributor




            Rocus Halbasch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
            Check out our Code of Conduct.






            $endgroup$













            • $begingroup$
              Hi Rocus, welcome to PSE. Please hide your answers using ">!"
              $endgroup$
              – Greg
              13 hours ago










            • $begingroup$
              Yeah. Just figured out how that works. This was my first answer.
              $endgroup$
              – Rocus Halbasch
              13 hours ago










            • $begingroup$
              No problem. Happy puzzling!
              $endgroup$
              – Greg
              13 hours ago














            1












            1








            1





            $begingroup$

            You can notice




            r2c1, r7c1, r3c5, r7c5 form a finned X-Wing for 4.




            Thus




            Consider r2c1. It must be either 4 or 8. If r2c1 is 4 that forces r3c3 to be 6. If r2c1 is 8 that forces r7c1 to be 4 which forces r7c5 to be 8 which forces r3c5 to be 4 which forces r3c3 to be 6. So if r2c1 is either 4 or 8 r3c3 is forced to be 6.




            Hopefully you can get it from there.






            share|improve this answer










            New contributor




            Rocus Halbasch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
            Check out our Code of Conduct.






            $endgroup$



            You can notice




            r2c1, r7c1, r3c5, r7c5 form a finned X-Wing for 4.




            Thus




            Consider r2c1. It must be either 4 or 8. If r2c1 is 4 that forces r3c3 to be 6. If r2c1 is 8 that forces r7c1 to be 4 which forces r7c5 to be 8 which forces r3c5 to be 4 which forces r3c3 to be 6. So if r2c1 is either 4 or 8 r3c3 is forced to be 6.




            Hopefully you can get it from there.







            share|improve this answer










            New contributor




            Rocus Halbasch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
            Check out our Code of Conduct.









            share|improve this answer



            share|improve this answer








            edited 13 hours ago





















            New contributor




            Rocus Halbasch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
            Check out our Code of Conduct.









            answered 14 hours ago









            Rocus HalbaschRocus Halbasch

            112




            112




            New contributor




            Rocus Halbasch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
            Check out our Code of Conduct.





            New contributor





            Rocus Halbasch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
            Check out our Code of Conduct.






            Rocus Halbasch is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
            Check out our Code of Conduct.












            • $begingroup$
              Hi Rocus, welcome to PSE. Please hide your answers using ">!"
              $endgroup$
              – Greg
              13 hours ago










            • $begingroup$
              Yeah. Just figured out how that works. This was my first answer.
              $endgroup$
              – Rocus Halbasch
              13 hours ago










            • $begingroup$
              No problem. Happy puzzling!
              $endgroup$
              – Greg
              13 hours ago


















            • $begingroup$
              Hi Rocus, welcome to PSE. Please hide your answers using ">!"
              $endgroup$
              – Greg
              13 hours ago










            • $begingroup$
              Yeah. Just figured out how that works. This was my first answer.
              $endgroup$
              – Rocus Halbasch
              13 hours ago










            • $begingroup$
              No problem. Happy puzzling!
              $endgroup$
              – Greg
              13 hours ago
















            $begingroup$
            Hi Rocus, welcome to PSE. Please hide your answers using ">!"
            $endgroup$
            – Greg
            13 hours ago




            $begingroup$
            Hi Rocus, welcome to PSE. Please hide your answers using ">!"
            $endgroup$
            – Greg
            13 hours ago












            $begingroup$
            Yeah. Just figured out how that works. This was my first answer.
            $endgroup$
            – Rocus Halbasch
            13 hours ago




            $begingroup$
            Yeah. Just figured out how that works. This was my first answer.
            $endgroup$
            – Rocus Halbasch
            13 hours ago












            $begingroup$
            No problem. Happy puzzling!
            $endgroup$
            – Greg
            13 hours ago




            $begingroup$
            No problem. Happy puzzling!
            $endgroup$
            – Greg
            13 hours ago


















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