Is there a knack to solve sudoku?

Question

Is there a knack to solve sudoku?

Answer 1

Indeed, with each solved sudoku your get more skills. Start from simple and just solve it.

Suggesting http://the-sudoku.com - Sudoku of different levels

Answer 2

Yes, but with practice you get the hang of it.  You will get faster and faster with practice.  Don't give up.  I have a book in the bathroom, every time I sit, I do a puzzle.

Answer 3

One of the things I do, besides using the processes of elimination the previous responder mentioned, is that I put in each cell, not the numbers it could be, but the numbers it couldn't. I do this by putting a series of dots in the cell corresponding to the numbers I have eliminated. I imagine the following diagram in each cell:

1 - 2 - 3

4 - 5 - 6

7 - 8 - 9

If I know the number in a particular cell cannot be a "1", I put a dot in the upper left corner of that cell. I do this for all numbers I have eliminated. When I have eight dots in a cell, I know exactly what belongs in that cell, by process of elimination.

The first thing I do is, I process each 3 x 3 square. If there are the numbers 1, 4, 5, 8 and 9 in five of the cells in the square, I will put dots in the upper left, center left, center center, lower center, and lower right positions of each of the blank cells. This shows I have eliminated those numbers in each of those cells.

Then I process each row in the same way, followed by each column. When I finish, I will almost always see cells that have eight dots in them. The empty position indicates the number that should go in the cell. I write in the number, then immediately place dots in the remaining cells in the square, row and column I just filled in. This may create a chain reaction of cells with eight dots. I must fill in each square and place the dots methodically; if I fill in several cells without marking the squares, rows and columns corresponding to that cell, I will lose track, and I will have to process each square, row and column as I did at the beginning. This can get frustrating, so I make sure I do this part methodically.

Once this process is complete, unless it is a ridiculously easy (level 1) puzzle, there will be cells that still have not been filled in. Then I start looking for ordered pairs and triplets as the previous responder suggested. If I find two cells in a square, row or column that are missing only the same two dots, the rest of the cells in that square, row or column cannot contain the two numbers corresponding to those dots. So I fill in those two dots in the remaining cells. I do the same for three cells that are missing the same three dots. It is rare to have a group of four missing dots, but I look for those also. Depending on how many ordered pairs and triplets you find, you may have to repeat this process until no more ordered pairs and triplets can be found.

Next, I look in each square, row or column for cells that have unique missing dots. For example, if a "7" is missing in a column, and only one of the cells in that column has a missing dot in the lower left corner, then I know that cell must be a "7".

I may have to alternate looking for eight-dotted cells, ordered pairs / triplets and unique missing dots several times until either the puzzle is solved or I am satisfied there is nothing further to be gained from this process. Once I have gotten to this point, I may have to grab a pencil that can be erased and try one of the numbers in a cell that contains only two missing dots. I will solve the rest of the puzzle with a pencil until either the puzzle is solved or I realize I originally entered the wrong number.

I hope this works as well for me as it does for you. Good luck! - LJS

Answer 4

Yes - Use a process of elimination, starting with an easy puzzle.

Once you have a number, it cannot appear in the same row, same column or same 3x3 box.

Start to list the possibilities in each empty box where you have many (6 or more) numbers already established in the row, column, or 3x3 box.

When you have your possibilities listed for an entire row, column or 3x3 box, if any cell includes a number that the other's don't, you have your answer for that cell.

When you have a situation where you know a cell can be one of two numbers, and another cell in the same row, column or 3x3 box can be one of the two same numbers, no other cell in that row, column, or 3x3 box can be one of those two numbers.  This logic follows for 3 cells that share possible numbers.

As you go on to harder puzzles, your list of possibilities per cell may grow substantially.  You must also "try out" some of your possibilities throughout the puzzle to see if it continues to be correct.  When you hit this stage, you may want to use different colored pencils to indicate testing a possibility.