## Difficulty of puzzles

Everything about Sudoku that doesn't fit in one of the other sections

### Difficulty of puzzles

I've been doing sudoku for about 6 months, and have moved from easy to medium to hard to evil at Web Sudoku. I'm now able to handle the evil ones well. I've also done a couple of diabolical puzzles at Sudoku Online. These felt about the same as evil. I'm wondering (1) what is the next step in difficulty, and (2) In general, what are the typical solving strategies required for the evil / diabolical puzzles and what are needed for more advanced puzzles?

Thanks,
Ken
kf-ryan

Posts: 3
Joined: 26 August 2005

If you look around here you will find a lot of threads with links to harder puzzles and an own forum for advanced solving technics.
Wolfgang

Posts: 208
Joined: 22 June 2005

If you approach these puzzles with nishio in your armoury (ie trying a number and seeing if it leads to a contradiction) then they will all seem the same. However many of them are created to exploit logic tricks like xy wings or xyz wings or swordfish etc etc.

There is also the question of how difficult it is to find the appropriate trick within the context of the puzzle. I'm not sure whether setters take this into account when rating their puzzles.

I create puzzles, but not fiendish ones. My way of rating them takes into account the strategy required to solve them but also relies on the number of cells that can be filled in at any time. If there are only 3 or 4 cells that can be filled, then the puzzle will be harder, since it'll be harder to find those cells. if there are 8 to 10 cells that can be filled at any time, the puzzle will be fairly simple.
ab

Posts: 451
Joined: 06 September 2005

ab wrote:If you approach these puzzles with nishio in your armoury (ie trying a number and seeing if it leads to a contradiction)...

That is *not* Nishio! Nishio is: "If I place the number N here, will the rest of the matching digits be placeable?" It considers a single number, ignoring the rest. It is very human implementable -- in fact, it can often be used *without pencilmarks* -- , but it doesn't come up that often and is *not* very powerful. It will not replace forcing chains, swordfish, etc and will certainly not equallize all levels of puzzles. It is an older tactic that predates most of the advanced ideas discussed in this forum.

A good definition of Nishio is here. Astraware has an incorrect definition here that's causing confusion. (They're definition is indistinguishable from the definition of 'guesswork' -- but they list them separately. I told them of the error months ago and they said they'd fix it the next time they updated the site, that is, don't hold your breath.)

This tactic should be part of everyone's arsenal.
tso

Posts: 798
Joined: 22 June 2005