Sudoku Rules & Object of the game
The object of the game is simple: Fill in the empty cells!
Easy, right? Well, hang on a sec…there is one rule you must follow: no repeats are allowed in any row, column, or block. To put it another way - you must use all nine numbers in each row, column, and block.
OK, so what are rows, columns, and blocks? Glad you asked! Take a look at this diagram:
Here we see the same puzzle shown three different ways, in order to highlight the rows, columns, and blocks. Together, I refer to these as the 27 'houses'.
Filling in the empty spaces doesn't seem that hard, does it? Actually, very often it's not. Be careful, though - each empty cell has only one correct answer. In fact, you might say the object of the game isn't so much "filling in" the cells as it is "figuring out" what goes in them.
You see, the pre-filled cells are not random. They were deliberately placed there in such a way to ensure only one final solution to the puzzle.
It is the player's job to solve the puzzle, cell by cell, until there are no empty cells left!
Interesting fact: Because of the rules, every completed Sudoku puzzle will end up with exactly nine of each digit (nine 1's, nine 2's, nine 3's, etc).