Menu
Skip Navigation Links.

Medusa 3D Elimination
While the Medusa 3D Elimination is an extension of the Rectangle Elimination technique, the Medusa 3D Elimination technique enhances this approach by utilizing Medusa 3D chains. The Rectangle Elimination technique involves the following steps:

  • Identify a 3x3 square where all cells with a certain candidate are located in one row and one column within the square.
  • Find two cells outside of this square with the same candidate, one in the same row and one in the same column.
  • If there is a scenario where both of these outside candidates can be ON, all candidates inside the 3x3 square will be eliminated. This scenario is invalid, and we should remove the outside candidates that caused this scenario.

With the Medusa 3D Elimination technique, the two outside candidates should belong to a Medusa 3D and have the same color. To avoid the elimination of all inside candidates, we need to remove both outside candidates of the chain that are located in the same row and one in the same column, as well as all other chain candidates with the same color. All chain candidates with a different color are valid Sudoku solutions. This approach is similar to the Rectangle Elimination technique with two strong links.

The following images illustrate the use of the Rectangle Elimination technique (on the left) and Medusa 3D Elimination (on the right) with the same sudoku puzzle.
Medusa 3D Elimination Example Medusa 3D Elimination Example
The image on the right shows the Medusa 3D chain, which includes three red candidates ('8' in cell E3, '3' in E8, and '8' in C8) and three green candidates ('3' in E3, '8' in E8, and '3' in C8). To avoid the elimination of all candidates '8' (marked in orange) in the top left 3x3 square, all three red candidates should be removed: '8' in cell E3, '3' in E8, and '8' in C8.
Medusa 3D Example The next image shows another Medusa 3D Elimination example. The Medusa 3D chain has 13 red and 11 green candidates. All three orange candidates '3' in the central 3x3 square would be eliminated if two red candidates '3' in cells G6 and F7 were ON. Therefore, we should remove all red candidates.