Re: Difficult Killer Sudoku 28/8
Quote:
That was not true of Sat's KS. I reduced to to three possibilities and had to do T & E on each possibility.
I agree that Saturday's puzzle was more difficult. Many of the steps required to solve that puzzle are more difficult than the hardest step for the Friday puzzle.
Below are some images to show the difference, the first image is what I considered the only step that was a little more difficult, 4&5 are paired values in cell f4 and in cage f5(6), so we can remove 4&5 from the other cells in the central 3x3 box (and also from column f if required later). From this point it is very easy to complete.
The next 3 images are 3 consecutive steps from the Saturday Killer, each of these steps uses more advanced techniques than anything in the Friday puzzle, and there is still some more work to go before it is solved. These are not the only difficult steps, I just chose these as an example because they are consecutive steps that result in many cells being solved.
Friday 28/8 (Difficult)
Saturday 29/8 (Difficult)
In the blue shaded cells there is a cross-pair with value 4, it is not your usual cross-pair because it is spread over 4 columns so it is easy to miss. The value 4 must be in either cage a4 or c4, and in cage f4, so we can remove it from g4 & g5.
Saturday 29/8 (Difficult)
Another cross-pair (value 9)
Saturday 29/8 (Difficult)
This is similar to before, there is a cross-pair with value 2, 2 must be in cage a4 or c4 and must be in cells g4 or g5.
These 3 steps solve several cells and gets it to a point that is close to complete.
I know "cross-pair" is probably the wrong term to use, somebody in the forum had suggested a better term but I have forgotten what that was.