dailysudoku.com

[anu]

How to solve sudoku

[David Bryant]

Use your head. dcb

[Guest]

I'll try to give you an introduction. Imagine the display below being the top left corner of a sudoku puzzle.

aa ab ac xa xb xc ba bb bc
ad ae af xd xe xf bd be bf
ag ah ai xg xh xi bg bh bi
ya yb yc
yd ye yf
yg yh yi

Square aa is

* one out of nine squares in the top left region (the 3x3 quadrant)
* one out of nine squares in the top row
* one out of nine squares in the left column

When you try to determin what number goes into square aa, you have to look what numbers are already featured in the same region, row and column. The numbers 1 to 9 shall appear only once each in every region, row and column.

So if ya is 1, aa can not be 1. If xb is 3, aa can not be 3. And if ai is 5, aa can not be 5. And so on. Keep ruling out numbers until you find where they logically must go. Start by looking at the given numbers that occur frequently and see if there is a region (or row, or column) where there is only one possible square left for a certain number.

Further on, let's say that you have found that ag must be either 2 or 5, and ah also must be either 2 or 5. This means that 2 and 5 must go in these two squares, either way, and that you can rule out the numbers 2 and 5 from the rest of that row (xg, xh, xi, bg, bh and bi).

Similarly, lets say that you have found that in the top left region, number 3 can only be placed i two squares: either aa or ab. This means that you can rule out 3 from the rest of that row (xa, xb, xc, ba, bb, and bc.

Hopefully, this will get you on the way. Good luck!