Find Hidden Twins
We have looked at the basic number finding strategies, but what if these are just not up to the job?
Until now we have been causally penciling in possible numbers, but there are many puzzles that will require you to be totally methodical in order to seek out and eliminate extraneous numbers.
If you have come to a point where obvious clues have dried up, you should ensure that you have actually found all the numbers that you can.
The first step towards achieving this is to pencil in all possible numbers in each square. It takes less time than you would think to rattle off “can 1 go”, “can 2 go”, “can 3 go” while checking for these numbers in the cell’s region, row, and column.
It never hurts to repeat the one basic tenet of the Sudoku puzzle:
Let’s look back to something that we looked at earlier: twins.
When you discovered the rule about “twins” the grid wasn’t so crowded as it is in section of the Sudoku grid below.
This time the twins are mixed with other numbers. It’s not obvious, but the two 1’s in the top region are twins. While you don’t know which cell is correct, you do know that the 1 in that region will exclude any other 1’s in column 3 right the way down to the bottom cell.
Using the twins strategy eliminates two 1’s in that column of the bottom region. Two 1’s in one region helped to eliminate 1’s in another remote region.
The more numbers that you can eliminate from a region the easier it will be to determine where these eliminated numbers go on the grid. Some cells have obvious number choices and this makes it easy for you to start solving the puzzle based on scanning and placing the numbers in the right cell.
It’s important to show you this, because while nothing is actually solved by this action, eliminating those 1’s could make all the difference in proving a number. You will be looking for things to help you move on in these kinds of crowded conditions. In a tough or diabolical puzzle it might allow you to proceed through to a solution without guessing.
