All Sudoku Variants
9×9 · Constraint

Argyle Sudoku

A set of diagonal lines crosses the grid in an argyle pattern; no digit may repeat along any marked diagonal.

2 5 8 3 6 9

An example Argyle puzzle: no digit repeats along each marked diagonal — here 2, 5, 8 and 3, 6, 9.

Argyle Sudoku draws a set of diagonal lines across the grid in the criss-cross pattern of an argyle sock or sweater. Along each marked diagonal, no digit may repeat — exactly like the diagonals of X-Sudoku, but there are several of them, running both ways, and most are shorter than the full corner-to-corner line.

The rule: no repeats along a marked diagonal

Wherever the argyle pattern draws a diagonal, treat it like an extra unit: every cell on it must hold a different digit. Below, one marked diagonal carries 3, 7, 1, 9, 5 — all different.

3 7 1 9 5

A marked diagonal (dashed): its digits 3, 7, 1, 9, 5 are all different.

A worked example, step by step

Take a marked diagonal that already shows a 3 and a 7.

3 7

Step 0. The diagonal shows 3 and 7; three cells remain.

Step 1 — the diagonal bans its own digits. Because no value repeats on the diagonal, the remaining three cells can be neither 3 nor 7 — on top of whatever their rows, columns and boxes already forbid.

3 7 ✗3,7 ✗3,7 ✗3,7

Step 1. 3 and 7 are barred from the rest of the diagonal.

Step 2 — stack the constraints. Each remaining diagonal cell also sits on its own row, column and box, so the diagonal ban combines with those to leave very few candidates — often a single one. Where two marked diagonals cross, a cell feels both diagonal bans at once, which is where Argyle puzzles crack open.

Why several short diagonals help

A single long diagonal (as in X-Sudoku) is a strong clue; a lattice of shorter ones spreads that strength across the whole grid. Even a three- or four-cell diagonal bans its digits from each other, and because the argyle lines overlap, many cells lie on two diagonals at once. Tracking which diagonals a cell belongs to is the key skill.

Solving strategy

  • Treat each diagonal as a unit. Scan it for repeats exactly as you would a row or box.
  • Target the crossings. A cell on two marked diagonals carries two extra bans — start there.
  • Combine with the grid. The diagonal ban plus the ordinary rules usually leaves a cell one candidate.
  • Feed the grid. Each diagonal digit placed behaves like a given for its row, column and box.

Common mistakes

  • Missing a diagonal. Argyle marks several lines both ways — check every one a cell lies on.
  • Treating unmarked diagonals as constrained. Only the drawn diagonals carry the no-repeat rule.
  • Overlooking the crossings. The cells on two diagonals are the most constrained — don't skip them.
  • Forgetting ordinary Sudoku. Diagonal cells still obey their rows, columns and boxes.

Can I play it here?

Not yet — Argyle Sudoku isn't one of the puzzle types SudokuStreak generates for now. But you can learn its rules above, and there's plenty here to sink your teeth into meanwhile: