"Last Possible Number" Technique

What is the "Last Possible Number" Strategy?

"Last possible number" is a simple strategy that is suitable for beginners. It is based on finding the missing number. To find the missing number, a player should look at the numbers that already exist in the 3x3 block they are interested in, and in the rows and columns connected with it.

How to Find the Last Possible Number

Let's take a look at a specific example.

Pay attention to the highlighted cell at R8,C1 (Row 8, Column 1). To find its value, we must scan its entire block, row, and column.

Step-by-Step Analysis

1. Check its Column (Column 1): We can see this column already contains the numbers 1 (at R5,C1), 2 (at R7,C1), 4 (at R9,C1), 7 (at R1,C1), and 8 (at R3,C1).
2. Check its Row (Row 8): This row already contains the numbers 3 (at R8,C8), 4 (at R8C4), 6 (at R8C6), and 9 (at R8C9).
3. Check its 3x3 Block (Bottom-Left): This block also contains the numbers 1 (at R7C2), 6 (at R9C3), and 9 (at R9C2). (The numbers 2 and 4 are already accounted for in Column 1).

Find the Missing Number

Let's combine all the unique numbers that are in this cell's row, column, and block: 1, 2, 3, 4, 6, 7, 8, and 9.

The only number from 1 to 9 that is not on this list is 5.

Considering that numbers should not be repeated, the only number that must be put in this cell is 5.

Master This Key Technique

That is how the "Last possible number" technique works. Once a player has mastered it, they will begin to solve Sudoku puzzles easier and more quickly!