dailysudoku.com

[sweedy]

i found a very hard one in the archives. dailysudoku.com assures that there are no sudokus with multiple solutions.. well, i'm not so sure...i even put it in the sudoku draw- function to see what it says, and it also "thinks" it has multiple solutions ore no legal solution at all. I found about three solutions, so is it really their fault?

[someone_somewhere]

Hi,
If you are reffering to this one:

400570000
009800570
000001006
030000860
008609100
065000020
800400000
094003600
000085007

than I can help you:

8 in r6c6 - Unique Horizontal
4 in r5c2 7 in r6c7 - Unique Vertical
7 in r5c1 7 in r8c4 - Unique Horizontal
7 in r4c6 2 in r5c5 - Unique Horizontal
5 in r4c5 4 in r2c6 - Unique Vertical
4 in r6c5 4 in r4c9 - Unique Vertical
3 in r6c4 9 in r6c9 - Unique in 3x3 block
9 in r4c1 1 in r4c4 - Unique in 3x3 block
1 in r6c1 2 in r4c3 - Unique in 3x3 block
1 in r8c5 - Sole Candidate
9 not in r3c7, it is in r1c7 or r1c8 (Row on 3x3 Block interaction)
9 not in r3c8, it is in r1c7 or r1c8 (Row on 3x3 Block interaction)
6 not in r7c3, it is in r9c1 or r9c3 (Row on 3x3 Block interaction)
1 not in r7c2, Hidden Pair 5 7 in r3c2 and r7c2 (in Column)
2 not in r3c2, Hidden Pair 5 7 in r3c2 and r7c2 (in Column)
2 not in r7c2, Hidden Pair 5 7 in r3c2 and r7c2 (in Column)
8 not in r3c2, Hidden Pair 5 7 in r3c2 and r7c2 (in Column)
1 not in r1c2, Nacked Pair 1 2 in r2c2 and r9c2 (same Column)
2 not in r1c2, Nacked Pair 1 2 in r2c2 and r9c2 (same Column)
8 in r1c2 - Sole Candidate

and from here one, you can swim alone to the UNIQUE final position.

see u,

[sweedy]

thank you for your quick reply!
and guess what, while trying to answer you, by putting each further step down, i found my mistake: i copied it down wrong! i missed the one in r3c6! no wonder i couldn't solve it!