## Let's play the fourth Sudoku game at second level hardness

This is the fourth game play at second level Sudoku. You should find it a bit harder to solve. The most basic technique of row column scan for finding a valid cell won't be enough any more. After proceeding a few steps by using row column scan, you will find suddenly that you are no longer able to proceed further.

This is the point where we have to devise new techniques for finding a valid cell based on new logic of pattern analysis.

This is the hallmark of Sudoku game.

As you try to solve increasingly difficult Sudoku problems, you need to create and use more sophisticated pattern analysis techniques.

We will keep open the option for you to devise your own techniques to solve the game. You may solve the game on your own and check the solution given at the end of the session. If you are stuck, you may refer to our step by step solution process.

Or, you may decide to learn the new techniques straightaway from our detailed solution.

### The Sudoku second level game 4

If you feel the *need to brush up the basics of how to play Sudoku in more details*, you may go back to our * session 1* and

*or*

**session 2****of beginner level Sudoku game play***.*

**session 1, and session 2 of second level Sudoku game play**Our strategy will generally be to find a valid cell by row column scan and if it doesn't work then use more powerful techniques.

The first five valid digits we get by row vcolumn scan with no more success. While forming DSAs we are able to form no less than four cycles. The following are the valid digit successes. **R6C8 8**, scan R4, C9 -- **R7C6 2**, scan R8, R9 -- **R6C9 2**, scan R4 -- **R2C1 8**, scan R1, R3, C3 -- **R8C3 4**, scan R7, R9, C1, C2. The result is shown in the following board.

We will now go over to the next stage.

At this stage we score only three successes with the first two through DSA technique, but we have done a fair amount of DSA enumeration for the cells that will come useful later. The three successes at this stage are, **R6C1 5** DSA cancel -- **R6C2 3** DSA cancel -- **R7C3 3**, scan C1, C2, R9.

Let us produce the results achieved till now.

Proceeding further, **R8C1 7, **Cycle (1,6) in R4C1, R7C1 leaving only the cell R8C1 for 7 --** R9C3 5, **DSA cancel --** R9C8 7, **scan R7, R8 --** R4C8 3, **DSA cancel --** R4C9 7, **DSA cancel --** R3C9 1 **DSA cancel --** R8C9 9 **DSA cancel --** R2C9 3.** The situation till now is as below.

Proceeding further,** R7C8 1, **cycle (6,8) --** R7C1 6, **DSA cancel --** R4C1 1, **DSA cancel --** R4C2 6, **DSA cancel --** R7C7 8, **DSA cancel --** R8C7 6, **DSA cancel --** R7C2 9 **--** R8C2 1, **scan R9 --** R9C2 8** -- **R8C5 3**, DSA [3,6] in C5 -- **R2C5 6** -- **R8C4 8**, scan C6, R9 -- **R8C6 5** -- **R5C6 3** DSA cancel -- **R5C4 5** -- **R1C4 3,** scan R2, R3, C6 -- **R1C2 2,** DSA [2,5] in C2 -- **R3C2 5 ** -- **R3C3 7**, DSA [1,7] -- **R2C3 1** -- **R1C6 1**, scan R2, R3 -- **R6C6 6**, DSA cancel -- **R6C4 1** -- **R2C6 7**, scan C4 -- **R9C6 9**, DSA [4,9] in C6 -- **R4C6 4** -- **R4C4 9** -- **R2C4 2**, DSA [2,4] -- **R3C4 4** -- **R9C4 6** -- **R3C8 6**, DSA [2,6] in R3 -- **R3C7 2** -- **R2C7 9**, DSA [5,9] in R2 -- **R2C8 5** -- **R1C7 7** -- **R1C8 4**. End. Game solved.

#### A special note for you

*We haven't tried to optimize. So we feel that this more complex game is solvable by following an easier path.*

**You should try to reach one of the simpler solutions. **

Lastly, we leave a game for you to solve.

### A game for you to solve

We leave you here with a new game for you to solve. In our next session we will present its solution and another new game.

Enjoy.