Similarly, if a smaller square already has the digits 1 through 4 filled in, then the only possible digits left for the remaining squares in that smaller square are 5 through 9. For example, if a row already has the digits 1 through 8 filled in, then the only possible digit left for the empty square in that row is 9. One of the most important aspects of solving Sudoku puzzles is using logic to eliminate possibilities and narrow down the options for each square.

The difficulty of the puzzle is determined by the number of squares that are initially filled in, with harder puzzles having fewer numbers filled in.

The puzzle starts with some of the squares already filled in with numbers, and the rest of the squares must be filled in by using logic and deduction. Make sure to follow and view other videos Video by Sudoku Guy, owned by Sudoku Guy and not affiliated with. The objective of the game is to fill in the grid so that every row, column, and smaller square contains each of the digits one through nine only once. The grid is further divided into nine smaller squares of three by three, each of which must be filled with the digits one through nine. Sudoku is a puzzle game that consists of a grid of nine squares by nine squares. You can find many more puzzles on the internet, in a whole range of difficulty levels.Section 1: Understanding the Basics of Sudoku If you reach a contradiction (a repeated digit in a row, column, or block), you should retrace your steps and undo what you've done until you have no contradiction.Įxercise: Here is a Sudoku puzzle for you to try: Continue playing, using the strategies above and any other ones you discover. If no entries are forced, try to pick a box with the fewest number of possibilities and pick one of them. Similarly, a triple of cells having only three possibilities of entries between them will eliminate these entries in all other cells in a neighborhood of this triple. This will decrease the number of possibilities for the other cells in the neighborhood and help you get closer to a solution. What you can still gain from this observation is that those pair of numbers cannot occur anywhere else in the neighborhood. You might find that a pair of cells has only two options of entries, but don't know which goes where. One more complicated strategy is to look at pairs or triples of cells within a row, column, or block. You often need more complicated analysis methods to make progress, and sometimes you need to make a guess and proceed, backtracking if the guess results in a conflict. These two strategies are usually not enough to completely fill in a Sudoku grid. Once you've done this, the chosen number can be eliminated from being a possibility for any other cell in the neighborhood. If the digit can only be placed in one cell in the neighborhood, you should fill that cell in. Note all the cells in the row, column, or block in which the number can be placed without violating the One Rule. If a cell ends up having only one possible entry, it is a 'forced' entry that you should fill in.Īnother way to proceed is to pick a number and a row, column, or block. The most basic strategy to solve a Sudoku puzzle is to first write down, in each empty cell, all possible entries that will not contradict the One Rule with respect to the given cells. In fact, mathematical thinking in the form of logical deduction is very useful in solving Sudokus. Any nine symbols would serve just as well to create and solve the puzzles. The puzzle does not depend on the fact that the nine placeholders used are the digits from 1 to 9. When one hears that no math is required to solve Sudoku, what is really meant is that no arithmetic is required.

Strategies for solving sudoku