Tips & Strategy
Probably the most significant component of a puzzle's difficulty level is the kind of logic
needed to find a solution. An easy puzzle requires fairly simple logic, while a challenging
puzzle depends on advanced logic such as Disguised Pair or X-wing.
If a Sudoku puzzle had 80 starting (or seed) numbers, the solution would be trivial. If a puzzle
had fewer than 10 starting numbers, even the most sophisticated computer program would be
hard-pressed to find a solution. So the quantity of seed numbers comes into play the most at
either extreme.
An apparently easy puzzle is actually harder if simultaneous fill-ins are not readily found.
That is, if the next fill-in depends on the one before it, then arriving at a solution requires
more exhaustive searching.
Some common logic types:
Exposed Pair
Disguised Pair
X-wing