by QBasicMac » Thu Mar 02, 2006 8:34 pm
sudoku_n00b,
Here rows are number 1-9 starting at the top and going down.
Columns are numbered 1-9 starting at the left and going right.
Boxes are numbered 1-3 at the top 4-6 in the middle and 7-9 at the bottom.
OK, look at Box 7, see row 7, column 3. (r7c3)? It is a 4.
It is a 4, thus there can be no more 4's on row 7 or in Box 7, right?
Now r8c4=4 also. So no more 4's on row 8 or in box 8.
Well, Box 9 needs a 4 somewhere. Where can it go?
Right: Either r9c7 or r9c8.
But look up. Above r9c8 is already a 4! So it can't go here.
That leaves only one place: r9c8. You can write a 4 there now.
Keep looking for patterns like that. When there are no more, try this:
Take a row that has som numbers already placed. The more, the better. Then figure out what digits are missing. These have to go into the remaining cells. So one-at-a-time, look at the cells and see if you can eliminate all but one candidate.
For example if you had a row like this:
425 8-1 --3
Then you see that 679 are missing.
Look at the - in 8-1 and see if 6, 7, or 9 are impossible. IF TWO OF THEM are impossible, then it HAS to be the other one. Stick it there.
Well, give it a try and work hard. If you get stuck, post where you got to so we can help.
Mac