Sudoku 2 - Medium

SUDOKU #2

I'm going to repeat the info at the top of Sudoku #1, just in case you haven't seen that one yet.

I've been doing Sudoku for a while. There are a lot of people like me who have figured out some tricks or techniques that help them complete the puzzles. This page is not really for them. I met a woman recently who was just starting to try to do Sudoku. This page is for people like her. I'm not saying that I know every single trick, but I know enough to complete most puzzles.

The basic rules of Sudoku are that there is only one of each number in each row, column, and 9 square grid. There isn't any mathematics or arithmetic. If you know how to count from 1 to 9, then you can do these puzzles. All of the techniques are based on this rule.

Here is a sample Sudoku puzzle.

This is a medium difficulty puzzle, and it will allow me to show some examples of a few of the tricks that I've uncovered. I've added the letters below to the rows and columns in order to talk about each of the 81 squares. As a convention, I will talk about squares and boxes. There are 81 squares, but there are 9 boxes of 9 squares.

The first technique that I will use is the lines of influence concept. This is what I mean. There is a 1 at AJ and another at IR, so there can't be another 1 in row A or column R. So there has to be a 1 at BP.

There is a 4 in columns P and R, and there are 4s in rows G and H, so there has to be a 4 at IQ.

There is a 2 in column J and another in row I, so there has to be a 2 in HL.

There is a 3 in columns M and N, and there is a 3 in row I, so there has to be a 3 at HO.

There is a 6 in columns J and L, so there has to be a 6 in IK. There is a 6 in columns Q and R, and now there is a 6 in row I, so there has to be a 6 in HP. There is a 6 in column O, so there has to be a 6 in EM. The final 6 goes in GN. So there has to be a 1 in CN.

There is a 2 in rows E and F, and there is a 2 in column P, so there has to be a 2 in DQ. There is a 2 in columns P and Q, and there is a 2 in row H, so there has to be a 2 in GR.

There is a 3 in row F and in column P, so the 3 in box DP-FR is either in EQ or ER. That means that there can't be a 3 in row E in the other two boxes to the left. There already is one in the center box in row F, so the one in box DJ-FL has to be in row D at square DK.

There is a 7 in row I and one in column Q, so there has to be a 7 in HR. That means that there is a 7 in GJ, which leaves the 8 in HJ.

There is a 9 in rows G and I, so there has to be a 9 in HQ and therefore a 1 in HM.