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I have been playing Sudoku since last month and I already thought I was pretty good.

Then I came up to a puzzle that is driving me nuts. After several hours of hard work I got to this point:

|.24|395|.67|
|...|674|...|
|6..|821|..9|

|..2|149|638|
|...|2..|...|
|..3|75.|.9.|

|38.|962|..4|
|9.6|4..|.2.|
|24.|5..|9.6|

I have checked it with the comp program and it says it is hard and valid. So, what am I missing or what technique do I have to learn?
Xuba

Posts: 6
Joined: 30 April 2006

When you place pencilmarks (if you use that technique), in C1, R1,5,6, only 148 can go in those locations.
Hud

Posts: 570
Joined: 29 October 2005

I don't think you'll need a "new" technique for this puzzle unless you are unfamiliar with "pointing pairs". Consider the number 7 and column 1; there is only 1 place a 7 can go. (edit - actually, it doesn't even need a pointing pair due to how much of the puzzle is filled in, but somehow my eye is drawn to it that way)

This will then lead to a couple other placements. If you get stuck, look for some "naked singles" which is the only other nonobvious step I needed to use before I was done. (I never use anything close to full pencilmarks which is why I'll say they are sometimes nonobvious)
motris

Posts: 71
Joined: 13 March 2006

Thank you guys!

I am ashamed. It sure doesn't need any special technique. Once the pencilmarks stopped giving me the big numbers, I had to go one step further: pick a number and start looking for his unique cell.

After finding the place for 7 in C1, the rest is easy.

Thanks again.
Xuba

Posts: 6
Joined: 30 April 2006