PLAYING THE NUMBERS GAME: An interview with Universal's Mr. Sudoku
David J. Bodycombe, compiler of the Universal Sudoku, currently has his puzzles published in over 150 publications worldwide. He took a few moments to answer some of the more common questions asked by addicts of the game:
How do you decide the difficulty level of a particular puzzle?
This is not an exact science, but generally you can tell which puzzles require more thought and technique to solve than others. For example, regular players will have come across the situation where you know that two boxes contain, say, a 5 and 7 in some order. Even though you don't know which number goes where, that fact can still help you deduce definite information elsewhere. That trick wouldn't be used in a 1-star puzzle but it might crop up in a 3-star. In short, the harder the difficulty level, the more deduction you'll need.
How many clues can a 9x9 puzzle have?
As a very rough rule, the more given clues that the grid contains, the easier it will be to solve. It is possible for a 9x9 grid to start with just 19 numbers and still be able to solve it. I think this is pretty impressive given that you're completing the entire grid based on less than 25% of the information! However, most everyday puzzles have around 30 numbers – anything less than that is harder, anything more is quite easy.
Is it possible for there to be more than one solution?
No, I give enough numbers in the grid to ensure that only one answer is possible. Many beginners forget about the rule regarding the 3x3 boxes, so sometimes it looks like you've solved the puzzle when in fact you haven't. Be sure to check your answer thoroughly!
How can I check whether my answer is correct?
In order to be 100% sure, the best thing is to quickly check each row, column and 3x3 box to ensure they have all the numbers from 1 to 9. Alternatively, look at the solution in the newspaper the next day. I don't know of any quick way of checking by, for example, looking at a certain number of squares – I'd be interested to hear if anyone has such a method.
Are there differences in the sudokus printed in newspapers?
Most definitely. On the superficial level, you'll notice that some puzzles are symmetrical and others aren't. I tend to prefer the symmetrical format because it looks tidier, in the same way that crossword grids also have half-turn symmetry. However, the type of logic used by different compilers is also different.
Do you have to guess?
For my puzzles, guessing is unnecessary and possibly time-wasting. Sometimes if there are only two possibilities for a certain square, it's tempting to plump for one and hope for the best. Unless you only have a few squares left and can plan ahead, I'd advise against this. My personal opinion is that puzzles which require guesswork are unfair and detract from the beauty of the game. Not everyone agrees with my point of view and there are other sudokus printed which break this 'rule'.
I notice that some papers print 16x16 Monster puzzles. How do you solve them?
The rules are essentially the same – each row, column and 4x4 box must contain 16 different symbols: the digits 0 to 9 and the letters A, B, C, D, E, and F. My main tip for solving these is to work methodically – look at where any 1s can go, then consider the 2s, 3s, 4s etc. Since there are over three times as many boxes, it's more important to have a system rather than let you eye wander across the grid at random.
