Basic Sudoku Solving Techniques
Sudoku is a Japanese game that has a 3 by 3 board of "blocks" where each block is a 3 by 3 grid of squares just big enough to hold a single digit. The point of the game is to fill in all the squares so that each row, each column and each block has all nine digits with no repeats. When the game starts, some of the digits are filled in.
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Rows and Columns Almost Full
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Look for a row or column that has three of fewer blank spaces. Try putting the missing digits in the available spaces. Try all possible combinations. It may be possible to put one of the digits in only one of the places. For example, a row may have only two blank spaces and the numbers 2 and 7 are the only digits missing from the row. Try placing the 2 and the 7 in these two spaces to see if there will be a conflict. If the 7 cannot go in one of these two spaces it must go in the other one. Then the 2 can only go in the last remaining space.
Blocks Almost Full
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Look for a block that has three or fewer spaces. Try the missing digits in the spaces in all possible combinations. There may be a digit that can go in only one of the spaces. Fill in that digit and continue with the remaining spaces.
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Consider Each Digit
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Starting with the number 1, and continuing until you have tried all nine digits, look for two blocks in a row or column that have that digit but in which the remaining block in that row or column does not have the digit. There will be a single row or column in the block where the digit in question may fit. Try it in all of the available spaces and it may turn out that it can go in only one place.
Cycle the Tricks
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Once you have gone through all three tricks, the board will have changed. Start at the beginning and apply all of the techniques again. Techniques that failed the first time will succeed when the board has more numbers filled in. Keep doing this until the board is completely filled with digits.
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