The Empty Rectangle technique is an advanced Sudoku solving strategy that helps you eliminate candidates in certain complex scenarios. It involves identifying an "empty rectangle" within a block, and using it to eliminate candidates from other cells.
How to Identify an Empty Rectangle
An Empty Rectangle pattern consists of the following characteristics:
A rectangle formed by cells in two rows and three columns, or two columns and three rows, within a single block.
All cells within the rectangle must not contain a specific candidate number (X).
There must be a cell outside the block, but in the same rows/columns as the rectangle, that contains the candidate number (X).
How the Empty Rectangle Technique Works
If the above conditions are met, you can eliminate the candidate number X from the two cells at the ends of the "empty rectangle" that also see the cell outside the block containing the candidate number X.
Example of the Empty Rectangle Technique
Tips for Spotting Empty Rectangles
Look for rectangles formed by cells in two rows and three columns, or two columns and three rows, within a single block.
Focus on rectangles that do not contain a specific candidate number.
Check for a cell outside the block, but in the same rows/columns as the rectangle, that contains the candidate number.
