The New Sudoku Players' Forum

[Tumbleweed]

Am I missing something or do I need to guess?

<puzzle off the net, via my daughter, she got stuck and I cant get further either, but a sudoku app on my Palm tells me it is solvable at this point>

xx8 463 759
xx7 825 x16
x65 179 8x2

851 6x2 x7x
x32 xx7 x68
67x xx8 52x

xxx xx6 28x
x8x xx1 6x5
5x6 x84 x97

[scrose]

Using forcing chains, r1c1 determines r5c1.

Code: Select all

r1c1=1 => r7c1<>1 => r9c2=1 => r9c7<>1 => r9c7=3 => r2c7<>3 => r3c8=3 => r3c1<>3 => r3c1=4 => r5c1<>4 => r5c1=9
r1c1=2 => r8c1<>2 => r9c2=2 => r9c4<>2 => r9c4=3 => r6c4<>3 => r6c4=9 => r6c3<>9 => r5c1=9

[Tumbleweed]

Using forcing chains, r1c1 determines r5c1.

Code: Select all

r1c1=1 => r7c1<>1 => r9c2=1 => r9c7<>1 => r9c7=3 => r2c7<>3 => r3c8=3 => r3c1<>3 => r3c1=4 => r5c1<>4 => r5c1=9
r1c1=2 => r8c1<>2 => r9c2=2 => r9c4<>2 => r9c4=3 => r6c4<>3 => r6c4=9 => r6c3<>9 => r5c1=9

OMG!

At least I dont feel too bad about whether there was some logic I had missed.
Thanks

Tw

[Nick70]

Using forcing chains, r1c1 determines r5c1.

There is a much simpler chain:

Code: Select all

r8c3<>9 => r8c5=9 => r4c5<>9 => r4c7=9
r6c3<>9 => r5c1=9 => r5c7<>9 => r4c7=9
  - Put 9 in r4c7

It can also be found using coloring--you need three color pairs though.

[scrose]

I suspected that there must be an easier way. I was excited just to have found the "clean" chains that I did!