Example Puzzles and Solutions

The program is supplied with a directory of example puzzles to try. The directory on MacOS X is ~/Library/Sudoku. If this directory doesn't exist, the program will create it automatically and place the default puzzles there. You can, of course, enter and save your own puzzle manually as well.

Here we list some of these puzzles and their solutions using the program. They are graded in order of difficulty easiest to difficult to "not fun".

Easiest

These are the easiest puzzles tested: use of only the first heuristic, namely, spotting inconsistency or insufficiency among rows, columns or 3x3 areas, is needed.

(See list of heuristics here.)

Arizona Daily Wildcat: Tuesday, Jan 17th 2006

File: wildcatjan17

Steps

Solved in 73 steps.

Uses only Heuristic 1: Simple row, column or 3 x 3 area inconsistency/insufficiency.

Arizona Daily Wildcat: Wednesday, Jan 18th 2006

File: wildcatjan18

Steps

Solved in 81 steps.

Uses only Heuristic 1: Simple row, column or 3 x 3 area inconsistency/insufficiency.

Intermediate

Daily Telegraph January 19th "Diabolical"

File: dtfeb19

Steps

Solved in 178 steps.

This is from the Daily Telegraph newspaper archives at http://www.sudoku.org.uk.

Only requires Heuristics 1 and 2, i.e. simple consistency check for rows, columns and 3x3 areas, and the subset cover idea.

Difficult

Vegard Hanssen puzzle 2155141

This is puzzle number 2155141, the highest-rated puzzle (as of Jan 19th 2006) on the Top 10 list on Vegard Hanssen's webpage.

File: v2155141
Steps
Solved in 196 steps.

It has only one step that is difficult (line 56). (See the description here.) To get past line 55, it employs the boosted version of Heuristic 1 plus an assist from Heuristic 4.

Challenge 2 from Sudoku Solver by Logic

File: challenge2

Steps

Solved in 133 steps.

This is Challenge 2 from Sudoku Solver by Logic. (See also the harder Challenge 1 below.)

This puzzles requires multiple instances of Heuristic 1+ before succumbing to direct elimination methods. However, all of the inference chains are relatively easy to follow as they require no more than two pivots.

Not fun

These puzzles are not fun anymore. I wonder if they are tractable for non-computer puzzle solving. At some steps, they seem to require long chains of inference just to eliminate a single value.

Challenge 1 from Sudoku Solver by Logic

File: challenge1

Steps

Solved in 229 steps.

This is Challenge 1 from Sudoku Solver by Logic.

Under the default setting, the program gets to step 84 making liberal use of Heuristic 1+, i.e. chaining. To proceed further, you must set the 1+ limit, the length of the chains the program is allowed to use to derive a contradiction, to unlimited.