Extreme Sudoku!!! (websudoku deluxe: 84,231,096,945)?

Question

Anyone want to help introduce me to some new strategies or at least get me started? I'm looking more for how I can get a number in this particular position rather than the actual solution itself. Thanks!

x8x x*x 36x

5xx 2x3 xx8

x39 48x x5x

89x x*x x7x

4x6 x3x 5x9

x7x x*x xx6

x58 xx1 4xx

3xx 948 xx5

x41 x*x x*x

Answer 1

Here is an solving approach (not really a technique) I found at

http://www.subundle.com/etc/FAQ.htm

After making sure there is a solution for this grid.

( e.g. http://www.sudokuwiki.com/sudoku.htm  )

Marking the options up, and clean up all the naked pairs, triples. etc.

row2-colum2 (B2) have only two options:  1 and 6

Take 6, no problems  for at least 10 steps.

Take 1 -> E22 (r5c2=2), E67 C66 B51  (conflict with B21 )

So, solving may go on.  as B2 known.

Answer 2

Not sure how much this will help, but ...

The middle square of upper left box (under first 8

and next to first 5) can only be 1 or 6.

I tried first 1 (which didn't work) and then 6 (which did)

in a computer based solver I have.

This solver only makes "sure inferences", that is,

it only fills in numbers when there are absolutely

no other possibilities.  There is no "what if" logic

or backtracking.

Following the manual placement of the 6,

it then completed the puzzle in the following order.

( = means that position was given ).

So in this case, except for that one square,

no other "what if"s were needed.

Without that try, it could not deduce anything.

What the following  means is:

the position labeled "1" (near lower left)

was the first box filled, and the one next to it labeled "2"

was the one after that, and so on.

Sorry about the formatting - there's only so much you can do here.

26  =  10  | 45  42  43  | =  =  11

=  =  7  | =  27  =  | 37  8  =

38  =  =  | =  =  5  | 29  =  25

=  =  19 | 35  30  12  | 28  =  18

=  4  = | 22  =  39  | =  23  =

9  =  17 | 46  44  47  | 21  13  =

14  =  =  | 40  36  =  | =  24  31

=  1  2  | =  =  =  | 6  3  =

16  =  =  | 33  34  32 | 15  20  41

You can go through those and figure out what

"8 out of 9" elimination it used for each position

and that might be of some help.

For example, for the first box numbered

(middle of lower left 3x3),

from the numbers in the 3x3, it can only be

2 6 7 or 9. Once 6 is placed top left middle,

6 7 9 are eliminated, and only 2 is possible.

The rest are eliminated by the column it's in.

Of course, when solving you don't know which

boxes will have "8 out of 9" logic applicable.

The best thing is to work on the squares

which are most constrained first.

For what it's worth, here is the solution.

1  8  2 | 5  7  9 | 3  6  4

5  6  4 | 2  1  3 | 7  9  8

7  3  9 | 4  8  6 | 2  5  1

8  9  5 | 6  2  4 | 1  7  3

4  1  6 | 8  3  7 | 5  2  9

2  7  3 | 1  9  5 | 8  4  6

9  5  8 | 7  6  1 | 4  3  2

3  2  7 | 9  4  8 | 6  1  5

6  4  1 | 3  5  2 | 9  8  7

.