How to Play Irregular Diagonal Sudoku

Irregular Diagonal Sudoku combines two variants: irregular jigsaw-shaped regions replace the standard 3×3 boxes, and both main diagonals of the 9×9 grid must each contain 1–9 exactly once. Cells on a diagonal therefore belong to four groups: row, column, jigsaw region, and diagonal. It is one of the most constraint-dense variants available.

A cell on one of the main diagonals belongs to four groups simultaneously: its row, its column, its jigsaw region, and its diagonal. The centre cell belongs to five groups — both diagonals, plus row, column, and region. This extreme constraint density makes every placement very powerful.

It is among the most constrained variants. The combination of irregular regions and diagonal constraints means almost every cell interacts with an unusually large portion of the grid. Expert puzzles in this variant are among the most demanding logic puzzles on the site.

Start with the diagonals, since diagonal cells carry the most constraints. Find hidden singles on each diagonal first. Then scan the jigsaw regions, keeping diagonal eliminations active. Update all four constraint groups — row, column, region, diagonal — after every single placement.

Yes — all standard techniques apply. You simply treat each diagonal as an additional house alongside the nine rows, nine columns, and nine jigsaw regions. The diagonal pointing pair (where a digit in a diagonal is confined to one row or column) is a particularly powerful technique unique to diagonal variants.

Easy puzzles take 10–20 minutes. Medium puzzles run 20–40 minutes. Hard puzzles average 40–75 minutes and expert puzzles often exceed 90 minutes. The combined constraint density means that even easy puzzles require tracking four constraint groups simultaneously.