About Sudoku

Wayne Gould thinks his Sudoku puzzles are beautiful. His wife thinks they are a bit of a doddle.

But there's no doubt the number puzzles have caught on with newspaper readers around the world.

The New Zealand Herald began publishing the puzzles in March, and following numerous requests from online readers they are now featured on nzherald.co.nz too (see link at end of this story).

The puzzles have gone from being a hobby into a retirement job for Mr Gould, a New Zealander who practised law for 13 years in Matamata before heading to Hong Kong where he worked as a magistrate and judge.

He reckons he can make the puzzles so tough that if a death-row inmate did one as a last request he'd be on a long reprieve.

The 59-year-old first found the patchwork puzzles in a bookshop in Tokyo's Ginza district.

The book was written in Japanese, but for the Hawera-born man who sees puzzles the same way a magpie does shiny trinkets, this was no deterrent.

"I think that is what makes a good puzzler, a willingness to keep nutting something out and resisting the temptation to go to the back of the book for the answers.

"The great thing about these puzzles is that they have to be solved by pure logic, not luck. They can be frustrating, but the reward when you crack them is a great feeling."

Mr Gould's Hong Kong retirement meant he soon had time on his hands again, and the challenge of coming up with a version of the puzzle was a perfect fit with another passion, codebreaking.

Once he'd got his head around the mechanics of the grid of columns, rows, and boxes strewn with seemingly random numbers, yet another personal passion tingled. This time it was computer programming.

He estimates his first Sudoku took about half an hour to crack, but his pet program to solve and generate a practically infinite number of the puzzles took six years. He eventually tested the program with about 25,000 different Sudoku patterns to ensure it could solve them all.

"I had been writing programs for leisure while working in Hong Kong," says Mr Gould. "But this project really swallowed up the hours. Luckily I was retired by then. You just don't have that much spare time when you're writing a judgment that could send someone to prison for 20 years."

The next step was to make sure the puzzles created by his program worked.

"I used to use my wife Gaye to test them. Unfortunately, after all that experience she is now much better at solving them than I am. She really has got it down to a fine art and can do an easy puzzle in about 90 seconds. It still takes me about three minutes."

A new puzzle is published every day in the New Zealand Herald and the Herald on Sunday, while the Monday-Friday puzzles also appear on nzherald.co.nz.

Throughout the week the difficulty increases, so if this Friday's proves a bit much, try next Monday for a return to a less difficult version. Solutions to each puzzle are available in the next day's newspaper as well as online.

How to play

The standard Sudoku formation is a grid of nine boxes, three deep and three high. Each box is divided into nine squares. Once solved every number from 1 to 9 appears once in each vertical column, horizontal row, and box.

Each puzzle has only one right answer. Try printing the puzzle, then pencilling in the number you think is correct in case you need to test another combination.

Mr Gould has tried to work out how many possible permutations there are, "but the maths got way beyond me".

The clues may seem random, but there is a definite aesthetic at work.

"I make sure they follow the Japanese style. They insist on having clues spread symmetrically so that it looks beautiful. Then it's not just a puzzle, it's a work of beauty."

Sudoku's origins are uncertain, but it may be based on the Latin Squares puzzle developed by 18th century Swiss mathematician Leonhard Euler.