What differentiates an easy sudoku puzzle from a hard one?

There are many different versions of a sudoku. Most standard sudokus are the regular kind in which it originated. Some versions have more combinations of correct answers based on the fact that there are more squares than the standard version. Instead of having just eighty-one squares in a nine by nine grid, there may be more. That alone would make it more difficult and time consuming.

However, there are other ways that some sudokus are more difficult than others. One of the main ways to find an easy sudoku is to find one that has more numbers in it. Many puzzles begin with numbers already written in them. However, fewer numbers or no numbers at all make it very difficult.