# Yuting Chen, Puzzle@home and the minimum information sudoku challenge

Sudoku comes from the Latin Square, invented in middle age, Leonhard Euler. But Sudoku related to the Colouring Problem, how do you colour each node in a pentagram/star so none have a neighbour the same colour. Think of Sudoku numbers as colours, each square must be different to its neighbour.

Solving sudoku for all sizes – it’s not just 9 x 9 – is an NP-complete problem, i.e “damn hard”!

How many solutions does Sudoku have? For 4 x 4 Latin Square, 576 versions, and for 9 x 9… there are lots and lots, i.e. 6 x 10 ^ 21. Without symetries, Russell & Frazer found 5.4bn solutions if you take out the symmetries.

Sudoku puzzles require clues to define a unique solution. With 4 clues, it might not have a unique solution. So what is the minimum number of clues that will provide a unique solution. Minimum found now is 17. But is there a 16 clue puzzle? Need a sudoku-checker programme to see if any 16 clue puzzles have unique solutions.

If can check for each solution in 1 second, need to spend 173 years to check all the options, but 1 second to search is not feasible.

Fastest checker will still take 2417 CPU years. Volunteer computing can help. Each solution can be checked independently.

Asia@home is promoting volunteer computing in SE Asia.

Future plans include earthquake hazard maps and medicine design simulations.