Found solution by trial and error, was there a logic method?

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Found solution by trial and error, was there a logic method?

Postby Stephen M » Fri Mar 10, 2006 6:35 am

Here's the grid and my candidates:

Code: Select all
17     17      6   |    8     5     4   |  9     3     2
9      2       5   |    1     6     3   |  7     48    48
48     48      3   |    2     7     9   |  1     5     6
===========================================================
34     6       8   |   459    1     7   |  35    2     359
347    47      2   |   4569   49    56  |  358   1     3589
5      9       1   |   3      2     8   |  4     6     7
===========================================================
68     58      9   |   4567   34    2   |  356   47    1
16     15      7   |   456    348   56  |  2     9     3458
2      3       4   |   5679   89    1   |  568   78    58


I found a unique solution, but only by trial and error. Was there a logic approach that I missed?

Here's the catch: this is the upper right corner from the Samurai Sudoku published Mar 5. in the Washington Post. I solved the rest of the puzzle except for a few squares that depended on first solving the 9x9 above. All constraints from the rest of the puzzle are fully captured in the lower left 3x3 above (for instance, I know they're can't be an 8 in columns 1-3 of row H)....SO, assuming I haven't missed something, the above grid should be solvable by logic.

As an aside, is there a solver somewhere that lets you enter additional constraints? That is, one that starts the solution from a grid of candidates that you enter? The solver on this site rebuilds the candidate grid from the starting grid, I couldn't find a way to add additional constraints. This makes it less useful for solving individual 9x9 corners of samurai sudokus, since you can't include the info from the adjacent 9x9 blocks.

TIA,
-Stephen M
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Postby vidarino » Fri Mar 10, 2006 9:22 am

You have a naked triple 156 in row 8 (cols 1, 2 and 6). This eliminates 5 and 6 from R8C4, leaving a naked 4. The rest should come naturally. ;)
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Postby Stephen M » Fri Mar 10, 2006 7:09 pm

Thanks!

I swear I have a blind spot for triples. Doesn't help that I'd been staring at it for far too long.
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Postby tarek » Fri Mar 10, 2006 8:08 pm

Stephen M wrote:blind spot for triples.

In the same row (row 8).........

You have also HIDDEN DOUBLE (38) which can solve the puzzle, a result which can be achieved using the Naked QUAD (1456)

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