Advanced sudoku games

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Easy Medium Hard Expert Evil. Auto-Check for Mistakes. Loading game. New Game Continue. Select Game Mode. Easy Medium Hard Expert Restart. Hard Sudoku puzzles Difficult Sudoku is for advanced players! Popular methods and techniques for solving hard web Sudoku Print difficult Sudoku and use different colors and symbols to solve it. Pros of playing hard web Sudoku puzzles The advantages of free web difficult Sudoku puzzles are obvious.

Cookie Preferences. It is a Sudoku at a stage where all the easy squares have been allocated. The light green squares are of interest, they are Bd that can be only [2,7]; Ce that can take [2,5] the 9 is not possible because of the naked twin [4,9] in row C and Ch that can take [5,7] the 9 is excluded for the same reason. So we have our chain [2,7] [7,5] [5,2] of three squares. The last two form the stem of the hook and 7 is the hook number.

Following our logic if the 2 went in Ce this means a 7 must go in Bd and a 5 in Ch. So this gives us the following segment of the grid.

The green squares are the ones we have tentatively allocated and the blue squares indicate where a 7 can not be allocated. The only other option for Ce was for it to be a 5 rather than a 2, and this forces us to put a 7 in Ch. So now we have the alternative scenario with Ch and Ce highlighted in green and for this alternative the blue squares show other squares which can not take a 7. Well, we are in luck as there are two squares which are blue in both the alternatives, that is square Bh and Cf - which we have highlighted in dark blue.

Square Cf is not particularly helpful because we already knew a 7 could not go there - there is a 7 in column f Square Gf. Square Bh can not be a 7 for either of the only two possibilities available for Ce 5 or 2 and so 7 can be safely excluded from the possibilities for this square. In the case of this particular puzzle, this is crucial, as that leaves only one choice for Bh as it can not be a 7 it must be the remaining possibility of 9, the hook strategy enables us to immediately solve a square and it turns out to be the last tricky one to be solved.

The Sudoku Hook is a general technique, the term X-Y Wing name comes from its mathematical formulation as three squares containing [x, y]; [y, z] and [x, z]. It tells us that the shared squares where the two alternative allocations for z intersect can not possibly contain a z.

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All you need to do is regularly use the Help Update Check Read More. To download this puzzle and see it in Sudoku Dragon click here It has all the features you need to solve puzzles whether you are new to Sudoku or an expert.

F or generation and solution of Sudoku puzzles download and install Sudoku Dragon. It is the complete Sudoku package, including hints, guides, and many new puzzle types. Download our Sudoku puzzle solver for a free 23 day trial. F or a further in-depth guide click here. Many have welcomed the new challenge but some have asked for help.

So, as we increase the difficulty Super Fiendish, the time has come to present the essential techniques for solving the most difficult Sudoku puzzles. Please be reassured that all Sudoku puzzles published in the Times are always solvable by logical means.

Here we present the techniques that will help you solve the hardest puzzles using only logic and no guesswork. First a couple of preliminary points: if you have ever completed any Fiendish or Super Fiendish Sudoku, you will be familiar with noting down candidates or pencil marks.

Pencil marks are small numbers, usually written at the top of each unsolved square, listing all the possible values for that square. With many advanced techniques, the key is to spot patterns within your pencil marks to eliminate possibilities within other squares. Whenever you solve a square, you must remove that number from the pencil marks in all other squares in the same row, column and block.

Essentially, this method uses the fact that in certain cases, there are only two possible ways of placing two numbers in four squares which form a rectangle.

The term x-wing itself derives from the x-wing fighters in Star Wars. The Sudoku in Fig. By doing this, you can eliminate the selected number from being an option for any other cell in the neighborhood. It is not always possible to completely fill in a Sudoku grid using these two strategies alone. Making progress often requires more complicated analysis methods, and sometimes a guess needs to be made, followed by backtracking in case the guess is wrong. An even more complex strategy is to view pairs or triples of cells within a row, column, or block.

In addition to decreasing the number of options for the neighboring cells, in this way, you can also get closer to an answer.