The New Sudoku Players' Forum

[piglet]

Someone has given me these. I have tried everything including x-wing and swordfish and I still can't crack them. What am I doing wrong?

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

0 0 9 8 3 0 4 0 0
0 2 0 0 4 0 0 8 0
0 0 0 0 6 5 1 0 0

0 0 0 0 9 0 7 0 4
0 0 0 3 0 0 0 0 9
9 5 0 4 2 7 3 0 8

and

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

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

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

[Nick70]

You are doing nothing wrong. Those two problems cannot be solved with techniques up to Swordfish.

Turbot Fish will allow you get farther, but it's still not enough. You'll need Double Forcing Chains, or Advanced Coloring.

The second one is quite interesting because it can be completely colored with a single color pair, placing 32 numbers out of 34 in a single step.

[piglet]

Thank you. Were can I learn about these techniques? I've come across colouring before but I didn't understand it. Never heard of Turbot fish!

[scrose]

This thread in the programmers' forum contains some examples of advanced colouring. The Turbot fish is described in this thread.