Sudoku grid | Contestants at our Sudoku competition | Tan Zek Gian from Raffles Girls's School receiving the first price from Professor Zhu Chengbo |

The Department of Mathematics, National University of Singapore organized the first ever Sudoku competition in Singapore during our Mathematics Enrichment Camp of Tuesday, December 13, 2005. We had almost 250 contestants and the winner was Tan Zek Gian from Raffles Girls' School (Sec 2).

Since then there have been several Sudoku competitions in Singapore. In 2006 I created the puzzles for the first national Sudoku competition in Singapore, the Sudoku Super-Challenge 2006, jointly organized by the Singapore Mathematical Society and the People's Association. In 2007 I served as Chief Judge for Chief Judge for the Brand's Sudoku Challenge Singapore 2007, a national competition with a $10,000 top cash prize.

I regularly hold lectures on Sudoku. You can download a copy of the lecture notes.

Sudoku is a logic puzzle where you are given a 9×9 grid made up of nine 3×3 blocks. The goal is to place the numbers 1 through 9 into the cells in such a way that each row, column and box contains each number exactly once. Some of the cells are given, and this is done in such a way that there is a unique way to fill in the remaining cells. The puzzles can be of varying levels of difficulty. They can be easy enough to appeal to anybody, while a mathematician will immediately be fascinated by the more fiendish puzzles and start thinking about algorithms.

Sudoku was invented in the US in 1979, but it only became popular when it was introduced in Japan in 1984. It took the UK by storm in late 2004 and quickly became a staple in most British papers. Here in Singapore the Today newspaper has a simple Sudoku on weekdays and a harder puzzle in the weekend edition. Many bookstores have a large selection of books with Sudoku puzzles.

I will describe some of the techniques for solving this puzzle and we will solve some puzzles together.

- Scanraid's Sudoku solver allows you to step through the solution and shows which techniques it uses.
- Sudoku Solver by logic.

Helmer Aslaksen

Department of Mathematics

National University of Singapore

helmer.aslaksen@gmail.com

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