## Introduction

SourGumdrop is a Sudoku playing program that can help players learn new techniques for solving puzzles.

Beginners can benefit from its quick and simple user interface and its range of helpful options. Experienced solvers can use its automatic filtering techniques to allow themselves time to concentrate on the more interesting and challenging components of puzzles. Beginners and experienced players alike can take advantage of the program's range of hint options. As the source code of the program is available programmers can change the program in any way they please.

The Overview page gives a good idea of some of the program's main features. Of course the only way to really know if you like a program is to try it...

To underpin the program's hint methods this website aims to provide clear explanations of the patterns used to solve puzzles. So far, thirteen common patterns are described and explained.

### Features

• An easily-used puzzle solving interface
• Hints for hidden singles, hidden pairs, hidden triples, locked candidates, naked pairs, naked triples, naked quads, xwing, swordfish, jellyfish
• Built-in puzzles
• Difficulty ratings
• Puzzle saving
• Undo mechanism
• Error checking
• Alternative grid sizes available
• Source code included

### A typical screendump

Figure 1. A screen dump from SourGumdrop showing a Naked triples hint. The pattern of candidates shaded in green allows the removal of the candidates coloured in red.

## News

### January 9th 2012

A proof that there are no 16 clue Sudokus has been submitted. There is also a Nature Comment article entitled Mathematician claims breakthrough in Sudoku puzzle. So if this proof survives scrutiny (and because of the necessarily brute force computational component of the proof this will be very difficult!) we will know that the minimum number of clues for a Sudoku puzzle is 17.

### February 18th 2011

Latest changes described here.

### August 21st 2008

Noticed that Gordon Royle now has 47793 17 clue Sudoku puzzles so redid my statistical analysis.

### May 30th 2008

Sourkoban, a Sokoban program released.

### April 16th 2008

Version v0.64 released. Search strategy selection not working. Fixed.

### April 10th 2008

SourGumdropK, a Kakuro program based on SourGumdrop released.

### April 3rd 2008

Version v0.63 released. The default hint search strategy is now "simplest hint". The main change this release is embarrassing. While working on SourGumdropK, a Kakuro program, based on SourGumdrop, I noticed that the SourGumdrop puzzles had, at some stage, lost their difficulty ratings. This has been rectified. Please note that the prefered contact email name has now changed to rodg.

### January 30th 2008

Version v0.62 released. Norman Hall requested the ability to group algorithms and to have a hint search strategy to find the simplest hint. He also wanted more control over the amount of information displayed about hints. His encouragement also got me round to adding the ability to save and read partially completed puzzles with their candidates. The "?" button in the Toolbar can now be used to execute hints (i.e. delete the candidates found) which means I can now click through a whole puzzle without moving my mouse - useful for testing! This latter change is not reflected in some screendumps used in the website. All these additions have been made and the documentation updated accordingly.

### January 1st 2008

Ian Millington The R'n'D Guy pointed out that my locked candidate 1 figure was ill chosen so I've replaced it. Thanks.

### October 18th 2007

I recently submitted the program to The Linux Game Tome and noticed a surge of Linux downloads so I've updated the documentation about how to set up SourGumdrop on Linux. Also changed the cascading style sheet to improve the look of the web site.

### May 19th 2007

SourGumdrop v0.60 released. Sudoku16 and Sudoku4 now possible: ie 16x16 and 4x4 grids. See: Alternative grid sizes

### May 13th 2007

SourGumdrop v0.54 released. Since v0.5 I have tidied up the configuration code, fixed a bug in which the wrong causes were shown for hidden triples, and another in the directed guessing solver. Added the option to colour candidates using the middle mouse button. Thanks to all those reporting bugs. None known at present.

### April 30th 2007

SourGumdrop v0.5 released. This is a complete rewrite of the program. New features: simpler, cleaner default look, but with a new configuration option which enables users to alter almost every component of the interface; new hint levels including the ability to show the candidates which form the pattern; simpler menu arrangements; timer; bug found and fixed in swordfish and jellyfish.

### February 12th 2007

SourGumdrop v0.4 released. Hidden triples was too restrictive - fixed. New option which allows the user to set scores for algorithms and to calculate puzzle difficulty. New puzzle entry window. Additional puzzle file format handled. New set of puzzles. New web pages describing the new features and giving statistics on an analysis of 36628 puzzles with only 17 clues. New versions of most screendumps. Improved descriptions of the solving methods.