Tips & Strategy

Likely 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.

Obviously 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