nightmare 10/19/06

tom_winget · Post by **tom_winget** » Wed Oct 25, 2006 5:44 pm

help me solve the nightmare. i cant find a way to solve it using logic, and i need to to prove someone wrong...

tom_winget · Post by **tom_winget** » Wed Oct 25, 2006 10:23 pm

sorry that last question was short. im in school and didnt have much time. my teacher doesnt believe me when i tell him that every sudoku puzzle with only one solution has a completely logical solution. can anyone help me with this particular nightmare?

Post by **Ruud** » Thu Oct 26, 2006 12:54 am

hi Tom,

I can give you an answer to your question regarding this particular Nightmare, but that does not prove that every sudoku has a completely logical solution. We only know that all known sudokus have a logical solution.

Here is the solving path for the October 19 Nightmare:

Code: Select all

Digit 9 is a hidden single for r2c9 in multiple houses
Hidden single in column 1 for digit 9
Box 2 only has candidates for digit 7 in row 1
Naked Pair in box 7 for digits &#40;7,8&#41;
Naked single for digit 6 in r9c1
Hidden Pair in row 2 for digits &#40;4,7&#41;
Hidden Pair in column 8 for digits &#40;3,7&#41;
Cells r2c8 and r2c5 trigger an Empty Rectangle in Box 6 Digit 6.
Two Almost Locked Sets sharing digit 1 eliminate candidate&#40;s&#41; for digit 4
The first ALS r5c1 r5c3 r5c5 r5c7 v12348 shares digit 1 with r6c8 v14. All cells that can see all digits 4 in both sets are eliminated.
Hidden single in column 9 for digit 4
Hidden Pair in row 6 for digits &#40;1,4&#41;
Empty Rectangle found in Box 7 Digit 8
Finned Jellyfish found for digit 8
3D Medusa Coloring. Targets can see both end colors of 2 bridged clusters.
An XY-Chain links r8c9 and r5c7 for digit 1
Hidden single in column 7 for digit 1
Digit 1 is a hidden single for r6c6 in multiple houses
Row 6 has one empty cell for the final digit 4
Hidden single in box 6 for digit 2
Box 6 has one empty cell for the final digit 6
Digit 2 is a hidden single for r2c7 in multiple houses
Column 7 has one empty cell for the final digit 5
An XY-Chain links r5c5 and r8c2 for digit 2
Hidden single in row 8 for digit 2
Column 2 has one empty cell for the final digit 1
Digit 1 is a hidden single for r8c9 in multiple houses
Column 9 has one empty cell for the final digit 8
Box 9 has one empty cell for the final digit 8
Last instance of digit 1 in r1c8
Hidden single in column 5 for digit 2
Box 5 only has candidates for digit 8 in row 4
Swordfish found in rows &#40;2,5,8&#41;, columns &#40;1,3,5&#41; for digit 8
Naked single for digit 6 in r4c5
Hidden single in row 2 for digit 6
Column 8 has one empty cell for the final digit 5
r3c6 causes an XY-Wing eliminating Digit 5
From this point, the puzzle can be solved with singles only.

Explanations for these techniques can be found in the solving guide on the main website.

Ruud

tom_winget · Post by **tom_winget** » Thu Oct 26, 2006 7:01 pm

i get it up to here

Digit 9 is a hidden single for r2c9 in multiple houses
Hidden single in column 1 for digit 9
Box 2 only has candidates for digit 7 in row 1
Naked Pair in box 7 for digits (7,8)
Naked single for digit 6 in r9c1
Hidden Pair in row 2 for digits (4,7)
Hidden Pair in column 8 for digits (3,7)

you lost me on the empty rectangle, though. could you provide me with a lengthy explanation for this problem, please. i would very much appreciate that, and, i also very much appreciate the help uv given me so far. thx.

p s - i get the empty rectangle technique from ur solving guide on this site, but couldn't find the application in this problem. can i get a diagram, cause i know that might help.

also, your beta program couldnt even get hidden singles when i tested it, so i think its got new bugs.

thanks for all ur help,
tom