Sudoku 14 - Evil

SUDOKU #14

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. It might be good to just print out this grid and write in the numbers as I go. There may be times when I do more numbers in one step than can be followed just by looking at the webpage.

This is a Evil difficulty puzzle (harder than Hard), 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.

There is a 6 in FJ (because of DP, EM, and GK). The numbers missing from box DM-FO are 2, 8, and 9. There is a 2 in DN (because of FL and EP). There is a 2 in AO (because of GM, DN, and BQ). There is another 2 in CJ (because of AO, BQ, and FL), and another one in IK (because of CJ and FL). The final 2 is in HR (because of BQ, EP, GM, and IK).

There is a 7 and a 9 in DJ and EJ (because of CK and HK), so the numbers missing from column K in box DJ-FL are a 1, 3, and 5. But there is a 1 in FM and a 5 in FP, so there is a 3 in FK, a 1 in EK (because of EO), and the 5 goes in DK.

There is a 9 in AM (because of CK, BP, and EN-FN). There is a 5 in BM (because of CQ, EO, and GN). There is another 5 in IR (because of CQ, FP, and GN). So there is a 5 in HJ (because of GN and IR) and another 5 in AL (because of BM, CQ, DK, and HJ).

There is an 8 in IJ (because of GQ and DL). There is a 6 in BL (because of CN, GK, and FJ). There is another 6 in AR (because of GK, DP, BL, and CN). There is a 4 in GJ (because of EL).

There is a 7 in CL (because of HK and DJ-EJ), and there is another 7 in IM (because of CL, FO, and AN-BN).

The number missing from column N are 1, 3, 4, and 7, but there is a 1 and 7 in row H. So there is either a 3 or a 4 in HN. The numbers missing from column P are 1, 3, 4, 7, and 8, but there is a 1 and a 7 in row H, and there is an 8 in GQ. So HP has to be either a 3 or a 4. So there cannot be a 3 in HM. Therefore, an 8 has to be in HM and a 3 in CM.

There has to be either a 3 or a 4 in IN (because of CM and CO), so there has to be a 1 or a 7 in AN and BN. Therefore, there is an 8 in BO.

There is an 8 in AK (because of IJ and BO), and a 4 is in BK. There is an 8 in CP (because of GQ), and a 1 is in CR.