Sunday, December 12, 2010

On Sudoku

I really enjoy sudoku nowadays, but I realize not everyone knows how to solve them.
This is an easy mini sudoku. See if you can fill all empty squares so that the number 1 - 4 appear once and only once in every row, once in every column, and once in every square box.

Start by putting 1 in the second row (row=across) and putting 3 at the bottom of the third column. And so on till you reach the final solution:

It's the same idea for the usual 9x9 sudoku puzzles, like these ones in the newspapers.

When I solve, I usually write small clues at the top of each box. It's like you have the options of putting 1 to 9, but then you start eliminating the choices.
Like for the game on the left, 3, 4, 6, 2, 5, 8 are in the first column so you can eliminate all those. Only 1, 7, or 9 can appear in the first column.

Then you can eliminate based on rows and boxes too.
Try solving sudoku with elimination clues.

By elimination, we know what can not be there.

Sometimes you can solve by noting what must be there: look at the top three rows, there is a 6 in the first box of nine, and there is a 6 in the second box, but the third box needs a 6 of its own. Since you noticed that the existing 6's are in the first row and the third row, then the needed 6 must be in the middle (second) row. It will be in the second row of the third box.

For more difficult sudoku sometimes you need more than just simple elimination. But not now.

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