🔷 How to play Antidiagonal Sudoku

By Miguel Arechaga

Antidiagonal Sudoku is a very elegant variant that imposes a surprising condition on the board's two diagonals: instead of requiring them to hold all different numbers (like Sudoku X), it demands the exact opposite, that they use very few numbers. It's a clever twist that opens up beautiful deductions. Here are the rules and a few tips.

What is Antidiagonal Sudoku?

It's a standard 9x9 sudoku with an extra condition on the two main diagonals (the ones running corner to corner, usually shaded). Each diagonal must contain only 3 different digits. Since each diagonal has 9 cells, that means each of those three digits appears exactly three times.

Rules and how to play step by step

1. The sudoku rules apply: 1 to 9 without repeats in each row, column and 3x3 box.
2. Antidiagonal restriction: each of the two main diagonals uses only 3 distinct digits (three times each).
3. You start with some clue cells and fill in the rest with logic. Every puzzle has a unique solution.

Tips to solve Antidiagonal Sudoku

• A diagonal touches the three boxes in its band: since each box contributes 3 cells to the diagonal and there are only 3 digits, those 3 cells in each box carry exactly the same trio of numbers.
• Find the trio early: as soon as you know two or three numbers of a diagonal, you know no others can appear, which rules out a great deal in rows, columns and boxes.
• The center cell belongs to both diagonals, so its digit is part of both trios.
• Combine the restriction with the classic elimination techniques of sudoku.

How it differs from regular sudoku

Compared to classic sudoku, Antidiagonal severely restricts the diagonals, the opposite of other diagonal-based variants, which demand all different values. If you enjoy variants with diagonal restrictions, you'll love comparing the two.