The New Sudoku Players' Forum

[Robert Craven]

How do they classify the difficulty of puzzles?
What makes a "hard puzzle" more difficult than a "medium puzzle"?
What does it take to make a puzzle very hard?

[scrose]

Usually the grade of difficulty is based upon what sort of techniques are required to solve a puzzle. With easy or very easy puzzles, there is often a cell that can contain only one number. Once you fill in that number, another such cell will appear, and so on until the solution is reached. Medium puzzles may require you to look for things such as the possibilities for a number occuring only in a row/column/block and being able to make eliminations based on that observation. Hard and very hard puzzles often require you to look for pairs or triplets of numbers and make eliminations based on those sets. The toughest puzzles contain devious patterns such as x-wings and swordfish. Essentially, the more complex the technique that is required, the greater the difficulty of the puzzle.