Sudoku 7 - Medium

SUDOKU #7

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.

Notice that there is a 7 and 8 in box AJ-CL in row A, and another pair in box AM-CO in row C, so there has to be a 7 and 8 in BP and BQ. There is an 8 in IP, so the 8 is in BQ and the 7 is in BP. That means that there is a 7 in EQ (because of GR and BP).

There is a 5 in AJ (because of FK and IL), another 5 in CN (because of AJ and BR), a 5 in HO (because of EM, CN, and IL), a 5 in DP (because of BR, FK, and EM), and the final 5 is in GQ (because of BR, DP, and IL).

There is a 3 in IR (because of AP and DQ), a 3 in GN (because of IR and HJ), a 3 in BM (because of GN and EO), a 3 in FL (because of HJ, DQ, and EO), and a 3 in CK (because of AP, BM, and FL).

There is a 1 in BO (because of AQ and DN), a 1 in FR (because of AQ, DN, and EJ), a 1 in CL (because of AQ and BO). There is a 1 in IM (because of EJ, DN, and BO).

The numbers missing from box AJ-CL are the 6 and 9, so there is a 2 in BN -- which means there is a 2 in AR (because of CJ and BN).

The numbers missing from box AP-CR are 6 and 9, but there is a 9 in FQ, so the 9 is in CP and the 6 is in CQ. That means there is a 4 in HQ.

The numbers missing from box GP-IR are the 1 and 6, which means the numbers missing from EP and FP are the 2 and 4, which means that the number in DR is an 8. There is an 8 in HK (because of IP, GM, and AL), an 8 in FJ (because of AL, HK, and DR), and there is an 8 in EN (because of FJ and DR).

There is a 1 in GK (because of AL and EJ) and another 1 in HP (because of GK).

There is a 6 in BL (because of IK) and a 9 in BK. There is another 6 in DJ (because of BL and IK). There is a 2 in EK, so there is a 2 in FP and a 4 in EP, and there is a 2 in HL (because of GO and IQ). The final 2 is in DM (because of FP and GO). There is a 7 in IJ, a 4 in GL, and a 6 in GP.