Double Sudoku
The puzzle Double Sudoku was introduced by Andrey Bogdanov during the Moscow Cup competition in 2011. Strictly speaking, it is not a standard Sudoku, as digits may repeat within rows and columns, yet its structure closely resembles one. The added no-touch constraint introduces an additional layer of logical reasoning, giving the puzzle a distinctive and elegant solving experience.
Rules
Place a digit from 1 to 4 in each empty cell so that each digit appears exactly twice in each row, column, and outlined region. Identical digits cannot share an edge.
Click to see the answer.