The New Sudoku Players' Forum

[Mex]

Code: Select all

.....3948
3.9..85..
..4.....2
5..9.....
..7.1.6..
.....7..1
692...1..
4387.12.9
1753.....

This is where i'm up to at the moment. But i am stuck and can't find anymore numbers. I found this puzzle on the sadman sodoku block/block interaction page http://www.simes.clara.co.uk/programs/sudokutechnique4.htm, it's the first one.
Anyway if someone can help me find a few numbers and go through the logic on how these numbers are obtained it would be very much appreciated.

Thanks,
Mex

[r.e.s.]

i am stuck and can't find anymore numbers. I found this puzzle on the sadman sodoku block/block interaction page http://www.simes.clara.co.uk/programs/sudokutechnique4.htm, it's the first one.

The easiest for you is probably to simply copy & paste this puzzle into the free software at http://www.angusj.com/sudoku/ and click the "Hint" button.

[Mex]

It can find out what the numbers are but doesn't really help. For example it says Hidden single for r3c7, so r3c7 = 3. But i don't see why it cannot be 7 also?

[rlangston]

Here's just one approach.... showing all candidates per cell....
With standard elimination you'd start with

Code: Select all

{27    }{1256  }{16    }{1256  }{2567  }{3     }{9     }{4     }{8     }
{3     }{126   }{9     }{1246  }{2467  }{8     }{5     }{167   }{67    }
{78    }{1568  }{4     }{156   }{5679  }{1569  }{37    }{1367  }{2     }
{5     }{12468 }{136   }{9     }{23468 }{246   }{3478  }{2378  }{347   }
{289   }{248   }{7     }{2458  }{1     }{245   }{6     }{23589 }{345   }
{289   }{2468  }{36    }{24568 }{234568}{7     }{348   }{23589 }{1     }
{6     }{9     }{2     }{458   }{458   }{45    }{1     }{3578  }{3457  }
{4     }{3     }{8     }{7     }{56    }{156   }{2     }{56    }{9     }
{1     }{7     }{5     }{3     }{24689 }{2469  }{48    }{68    }{46    }


Hidden Single: Digit 1 only found in one col (6 ) of row 8
With standard elimination:

Code: Select all

{27    }{1256  }{16    }{1256  }{2567  }{3     }{9     }{4     }{8     }
{3     }{126   }{9     }{1246  }{2467  }{8     }{5     }{167   }{67    }
{78    }{1568  }{4     }{156   }{5679  }{569   }{37    }{1367  }{2     }
{5     }{12468 }{136   }{9     }{23468 }{246   }{3478  }{2378  }{347   }
{289   }{248   }{7     }{2458  }{1     }{245   }{6     }{23589 }{345   }
{289   }{2468  }{36    }{24568 }{234568}{7     }{348   }{23589 }{1     }
{6     }{9     }{2     }{458   }{458   }{45    }{1     }{3578  }{3457  }
{4     }{3     }{8     }{7     }{56    }{1     }{2     }{56    }{9     }
{1     }{7     }{5     }{3     }{24689 }{2469  }{48    }{68    }{46    }


This is where you are.
Now....
Locked Candidates 2: In row 5 digit 3 appears only in the cells for box 6,
so the digit is removed from R4C7, R4C8, R4C9, R6C7, and R6C8 (within the same box).
And with standard elimination:

Code: Select all

{27    }{1256  }{16    }{1256  }{2567  }{3     }{9     }{4     }{8     }
{3     }{126   }{9     }{1246  }{2467  }{8     }{5     }{167   }{67    }
{78    }{1568  }{4     }{156   }{5679  }{569   }{37    }{1367  }{2     }
{5     }{12468 }{136   }{9     }{23468 }{246   }{478   }{278   }{47    }
{289   }{248   }{7     }{2458  }{1     }{245   }{6     }{23589 }{345   }
{289   }{2468  }{36    }{24568 }{234568}{7     }{48    }{2589  }{1     }
{6     }{9     }{2     }{458   }{458   }{45    }{1     }{3578  }{3457  }
{4     }{3     }{8     }{7     }{56    }{1     }{2     }{56    }{9     }
{1     }{7     }{5     }{3     }{24689 }{2469  }{48    }{68    }{46    }


Hidden Single: Digit 3 only found in one row (3 ) of col 7
With standard elimination:

Code: Select all

{27    }{1256  }{16    }{1256  }{2567  }{3     }{9     }{4     }{8     }
{3     }{126   }{9     }{1246  }{2467  }{8     }{5     }{167   }{67    }
{78    }{1568  }{4     }{156   }{5679  }{569   }{3     }{167   }{2     }
{5     }{12468 }{136   }{9     }{23468 }{246   }{478   }{278   }{47    }
{289   }{248   }{7     }{2458  }{1     }{245   }{6     }{23589 }{345   }
{289   }{2468  }{36    }{24568 }{234568}{7     }{48    }{2589  }{1     }
{6     }{9     }{2     }{458   }{458   }{45    }{1     }{3578  }{3457  }
{4     }{3     }{8     }{7     }{56    }{1     }{2     }{56    }{9     }
{1     }{7     }{5     }{3     }{24689 }{2469  }{48    }{68    }{46    }


Hidden Single: Digit 7 only found in one row (4 ) of col 7
With standard elimination, a lot clears out:

Code: Select all

{7   }{1256}{16  }{1256}{25  }{3   }{9   }{4   }{8   }
{3   }{126 }{9   }{1246}{24  }{8   }{5   }{16  }{7   }
{8   }{156 }{4   }{156 }{579 }{59  }{3   }{16  }{2   }
{5   }{18  }{13  }{9   }{38  }{6   }{7   }{2   }{4   }
{9   }{48  }{7   }{248 }{1   }{24  }{6   }{3   }{5   }
{2   }{46  }{36  }{45  }{345 }{7   }{8   }{9   }{1   }
{6   }{9   }{2   }{458 }{458 }{45  }{1   }{7   }{3   }
{4   }{3   }{8   }{7   }{6   }{1   }{2   }{5   }{9   }
{1   }{7   }{5   }{3   }{29  }{29  }{4   }{8   }{6   }


Hidden Single: Digit 7 only found in one col (5) of row 3.

Code: Select all

{7   }{1256}{16  }{1256}{25  }{3   }{9   }{4   }{8   }
{3   }{126 }{9   }{1246}{24  }{8   }{5   }{16  }{7   }
{8   }{156 }{4   }{156 }{7   }{59  }{3   }{16  }{2   }
{5   }{18  }{13  }{9   }{38  }{6   }{7   }{2   }{4   }
{9   }{48  }{7   }{248 }{1   }{24  }{6   }{3   }{5   }
{2   }{46  }{36  }{45  }{345 }{7   }{8   }{9   }{1   }
{6   }{9   }{2   }{458 }{458 }{45  }{1   }{7   }{3   }
{4   }{3   }{8   }{7   }{6   }{1   }{2   }{5   }{9   }
{1   }{7   }{5   }{3   }{29  }{29  }{4   }{8   }{6   }


Hidden Single: Digit 9 only found in one row (9) of col 5. And then
it clears out from there with standard elimination.

Another approach,starting from where you are...

Code: Select all

{27    }{1256  }{16    }{1256  }{2567  }{3     }{9     }{4     }{8     }
{3     }{126   }{9     }{1246  }{2467  }{8     }{5     }{167   }{67    }
{78    }{1568  }{4     }{156   }{5679  }{569   }{37    }{1367  }{2     }
{5     }{12468 }{136   }{9     }{23468 }{246   }{3478  }{2378  }{347   }
{289   }{248   }{7     }{2458  }{1     }{245   }{6     }{23589 }{345   }
{289   }{2468  }{36    }{24568 }{234568}{7     }{348   }{23589 }{1     }
{6     }{9     }{2     }{458   }{458   }{45    }{1     }{3578  }{3457  }
{4     }{3     }{8     }{7     }{56    }{1     }{2     }{56    }{9     }
{1     }{7     }{5     }{3     }{24689 }{2469  }{48    }{68    }{46    }


Hidden Pairs: 37 found in cols 8 and 9 of row 7 ; removing extra digit 4 from 9
Hidden Pairs: 37 found in cols 8 and 9 of row 7 ; removing extra digit 5 from 8
Hidden Pairs: 37 found in cols 8 and 9 of row 7 ; removing extra digit 5 from 9
Hidden Pairs: 37 found in cols 8 and 9 of row 7 ; removing extra digit 8 from 8
Hidden Pairs: 29 found in cols 5 and 6 of row 9 ; removing extra digit 4 from 5
Hidden Pairs: 29 found in cols 5 and 6 of row 9 ; removing extra digit 4 from 6
Hidden Pairs: 29 found in cols 5 and 6 of row 9 ; removing extra digit 6 from 5
Hidden Pairs: 29 found in cols 5 and 6 of row 9 ; removing extra digit 6 from 6
Hidden Pairs: 29 found in cols 5 and 6 of row 9 ; removing extra digit 8 from 5
Then various hidden singles.

Yet another approach would be to lean more heavily on naked triples:
Again starting as

Code: Select all

{27    }{1256  }{16    }{1256  }{2567  }{3     }{9     }{4     }{8     }
{3     }{126   }{9     }{1246  }{2467  }{8     }{5     }{167   }{67    }
{78    }{1568  }{4     }{156   }{5679  }{1569  }{37    }{1367  }{2     }
{5     }{12468 }{136   }{9     }{23468 }{246   }{3478  }{2378  }{347   }
{289   }{248   }{7     }{2458  }{1     }{245   }{6     }{23589 }{345   }
{289   }{2468  }{36    }{24568 }{234568}{7     }{348   }{23589 }{1     }
{6     }{9     }{2     }{458   }{458   }{45    }{1     }{3578  }{3457  }
{4     }{3     }{8     }{7     }{56    }{156   }{2     }{56    }{9     }
{1     }{7     }{5     }{3     }{24689 }{2469  }{48    }{68    }{46    }


Naked Triple: 458 in R7C4/R7C5/R7C6, R7C8 digit 5 not possible.
Naked Triple: 458 in R7C4/R7C5/R7C6, R7C8 digit 8 not possible.
Naked Triple: 458 in R7C4/R7C5/R7C6, R7C9 digit 4 not possible.
Naked Triple: 458 in R7C4/R7C5/R7C6, R7C9 digit 5 not possible.
Interestingly this reduces out the same candidates as does the hidden pairs 37
seen above. Then these....
Naked Triple: 486 in R9C7/R9C8/R9C9, R9C5 digit 4 not possible.
Naked Triple: 486 in R9C7/R9C8/R9C9, R9C5 digit 6 not possible.
Naked Triple: 486 in R9C7/R9C8/R9C9, R9C5 digit 8 not possible.
Naked Triple: 486 in R9C7/R9C8/R9C9, R9C6 digit 4 not possible.
Naked Triple: 486 in R9C7/R9C8/R9C9, R9C6 digit 6 not possible.
That reduces out the same candidates as the hidden pairs 29 seen above.

[r.e.s.]

It can find out what the numbers are but doesn't really help. For example it says Hidden single for r3c7, so r3c7 = 3. But i don't see why it cannot be 7 also?

Of course it helps -- once you understand what a hidden single is.
In this case, there is no other place to put a 3 in coulmn 7. (Both the site you mentioned and the one I mentioned discuss what these terms mean.)

[Mex]

Ok i got two extra numbers from where i started. Thanks! Except i can't see why r4c9 = 4

[bbsudoku]

You don't need to worry about the 7 because the only place available for 3 in the top right box is in R3C7.

The 3 can't be in R2C8 or R2C9 because of the 3 in R2C1
This leaves either R3C7 or R3C8

The 3 can't be in R4C7 or R6C7 because a 3 must be in one of either R4C3 or R4C5 and a 3 must be in one of either R6C3 or R6C5
This leaves a 3 in R5C8 or R5C9

The 3 can't be in R9C7, R9C8, or R9C9 because of the 3 in R9C4
This leaves a 3 in either R7C8, R7C9, or R8C9

So C8 is used up by a 3 in either R5, R7, or R8 and thus 3 can't be in R3C8

This leaves R3C7 as the only block that can hold a 3, so the 7 doesn't matter.

[bbsudoku]

OK,

R4C9 possibilities

1? No because of R6C9
2? No because of R3C9
3? No because we've already determined that 3 is in R5C8 or R5C9
4? Yes
5? No because of R4C1
6? No because of R5C7
7? No because of R4C7
8? No because of R1C9
9? No because of R8C9

All that's left is a 4

[Mex]

Thank you!

Didn't see the 5 =/.