The Difficulty Factor

Sudoku puzzles can vary in difficulty, even from person to person. But what exactly makes one more challenging than another? Numerous factors contribute to a puzzle’s difficulty. Whether you are creating a Sudoku and have a desired difficulty you are striving for, or if you’re simply someone trying to solve a Sudoku and want to be able to analyze if it will be difficult or not. I will highlight a few different techniques used in finding out if a Sudoku is easy or hard.

A Sudoku variant is a rule or an addition to the grid that introduces extra strategy into the puzzle. Some popular variants include the following:

How Many Given Cells Are There?

An effective way to understand a Sudoku’s difficulty at a glance is by looking at how many given cells are in the puzzle. As you might guess, a Sudoku with a small number of givens can be difficult compared to one with a large quantity of given cells. That is because if the puzzle has fewer givens, then it will also have less clues for you to go off.

In standard Sudoku, it is known that the minimum number of given cells in a puzzle is seventeen. However, that does not mean that the fewer Cells a puzzle has, the harder it will always be to solve. Puzzle setters know this and will sometimes create difficult puzzles that use a relatively large number of given cells to throw you off.

Pencil Mark Technique

The aim of this method is to figure out the Candidates in each cell. This can easily be done on most digital programs, though it is time consuming to attempt on a piece of paper.

Typically for easy puzzles, each cell will have a small number of Candidates. There is a technique when solving that uses Pencil Marking to discover cells that only have a single Candidate, cells like that will be immediately solved and you can write the Candidate down as the correct number. Therefore, being a hidden Given cell.

If the Pencil Marks reveal a lot of Candidates on each cell, that puzzle will be harder and usually require advanced solving techniques to crack.

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