﻿ Conceptis 数独 difficulty levels explained

# Conceptis Sudoku difficulty levels explained

Sunday, September 24, 2006

Recently I have been asked about the features which determine the difficulty of Conceptis Sudoku puzzles. But before I start to explain I’d like to make a statement some might find quite surprising: There is no connection between the difficulty of a Sudoku puzzle and the number of clues it contains. This is a myth. There are very hard puzzles with many clues and easy puzzles with very few clues. It is the number of logic decisions, their redundancy and their complexity which determines how hard the puzzle is going to be.

Take Ultra Easy, Very Easy and Easy Conceptis Sudoku puzzles for example. They require just the simplest “Scanning” solving techniques as described in our website under Sudoku >> Solution Examples. There is no need to count missing numbers in rows and columns, to note down pencilmarks, or to make any assumptions.

The difference between Ultra Easy, Very Easy and Easy puzzles is that more logical decisions are required and less immediate solvable clues are available as you progress. The Ultra Easy puzzles can be solved in less than 5 minutes while the Easy can take about twice the time.

## Necessary to use assumption logic

Medium and Medium Plus puzzles require the use of more advanced techniques. Here you need to use pencilmarks as well as count rows and columns, checking the numbers to see which ones are missing and where they can be placed. Again, the difference between Medium and Medium Plus is the frequency of logic decisions and the number of bottlenecks encountered during the solution process.

A bottleneck is a situation in the solution flow where only a single move is possible to continue the progress of the puzzle. Thus, if a puzzle has many bottlenecks then it becomes harder to solve even if the solving techniques are easy. Medium puzzles can take 20 or 30 minutes, while Medium Plus puzzles can take even more.

Solving Hard and Very Hard puzzles requires some really difficult techniques. In addition to scanning, pencilmarking and row/column counting, it now also necessary to use assumption logic where the solver presumes a certain cell contains a certain number and then checks if this is possible or not. Hard puzzles can take well over one hour, and I don't think I ever managed to solve a Very Hard puzzle on my own :)