Stuck on Hard Puzzle

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Stuck on Hard Puzzle

The following was in the Wilmington, Delaware "Sunday News Journal", January 21, 2007.

|7 1 0|0 0 5|0 2 0|
|0 0 0|0 8 0|0 7 0|
|0 0 3|0 0 0|9 0 0|
---------------------
|0 0 9|0 0 6|5 0 0|
|6 4 0|0 0 0|0 9 2|
|0 0 5|9 0 0|1 0 0|
---------------------
|0 0 1|0 0 0|8 0 0|
|0 6 0|0 7 0|0 0 0|
|0 5 0|4 0 0|0 3 1|

I can solve this puzzle without making any assumptions only thus far:

|7 1 0|0 9 5|0 2 0|
|0 0 0|0 8 0|0 7 0|
|0 0 3|0 0 0|9 1 0|
---------------------
|1 0 9|0 0 6|5 0 0|
|6 4 0|5 1 0|0 9 2|
|0 0 5|9 0 0|1 0 0|
---------------------
|0 0 1|0 5 0|8 0 0|
|0 6 0|0 7 0|0 5 0|
|0 5 0|4 0 0|0 3 1|

I can only solve the puzzle completely if I in insert a 3 in Row1, Column4.

The solved puzzle is:

|7 1 6|3 9 5|4 2 6|
|5 9 2|1 8 4|6 7 3|
|4 8 3|6 2 7|9 1 5|
---------------------
|1 2 9|1 3 6|5 8 4|
|6 4 7|5 1 8|3 9 2|
|8 3 5|9 4 2|1 6 7|
---------------------
|9 7 1|2 5 3|8 4 6|
|3 6 4|8 7 1|2 5 9|
|2 5 8|4 6 9|7 3 1|

Can you help me?

Leon Scott
LeonScott

Posts: 4
Joined: 11 February 2006

If you look in column 5, there has to be a 3 somewhere. Rows 1, 2 5, 7 and 8 are already taken. Row 3 already has a 3 at R3C3 and row 9 has a 3 at R9C8. There must, therefore be a 3 in either R5C4 or R5C6 - 'X'

Code: Select all
`|7 1 0|0 9 5|0 2 0||0 0 0|0 8 0|0 7 0||0 0 3|0 0 0|9 1 0|+-----+-----+-----+|1 0 9|0 X 6|5 0 0||6 4 0|5 1 0|0 9 2||0 0 5|9 X 0|1 0 0|+-----+-----+-----+|0 0 1|0 5 0|8 0 0||0 6 0|0 7 0|0 5 0||0 5 0|4 0 0|0 3 1| `

This leaves you a naked single 8 at R5C6 etc.
underquark

Posts: 299
Joined: 06 September 2005

Sorry, missed out a bit in the above. Eliminating the 3s as above leaves a bunch of hidden singles (though it but didn't write it down):

3 at R5C7
7 at R9C7 then R2C7 then R5C3
and then the naked single 8 at R5C6

After that it's mainly hidden and naked singles with, mayve, a pair thrown in for good measure.
underquark

Posts: 299
Joined: 06 September 2005