Argyle Sudoku (PuzzleMadness)

About Argyle Sudoku (PuzzleMadness)

Argyle Sudoku keeps the usual rules, 1 to 9 once in each row, column and 3x3 box, and adds eight diagonal lines drawn across the grid in a diamond lattice. Digits may not repeat along any line. It resembles X-Sudoku, but the diagonals are shorter: none of them runs the full nine cells, and the longest have eight.

That difference changes how the lines help. On an X-Sudoku diagonal every digit must appear once, so you can look for the only place a digit fits. On an Argyle line a digit need not appear at all, so the lines only ever remove candidates: once a digit is on a line, it is ruled out of every other cell on that line. Where two lines cross, a single cell sees both, and a lot of eliminations meet there.

The grid works like every sudoku on PuzzleMadness: number buttons above and below it, an eraser, and a pencil mode for candidate digits. On a keyboard, the number keys enter digits, the arrow keys move between cells, Ctrl, Shift or Alt with a number adds a pencil mark, and Delete or Backspace clears a cell.

PuzzleMadness is a free puzzle website run by Dewi, a software developer who started out making games for the PlayStation 2, Nintendo Wii and DS and now builds the site as a hobby. It carries dozens of puzzle types, from classic sudoku to newer logic grids, and each one gets its own dated puzzle every day at each difficulty. Argyle Sudoku comes in Easy, Medium, Hard and Tough versions plus a Mixed page, and the same day's Argyle Sudoku puzzle is shared by everyone who opens it.

The site checks your grid as you go and tells you when it is finished; it does not publish solutions. Each completed puzzle earns a score, and scores feed a monthly and an all-time Argyle Sudoku leaderboard, where only your best attempt at a puzzle counts. Older days stay in the archive, so a missed puzzle can still be played later and still counts toward the current month. Playing needs no account; a free registration gives you a username on the leaderboards and a cloud save. The pages carry adverts.

How to play Argyle Sudoku (PuzzleMadness)

1. Open today's Argyle Sudoku page on PuzzleMadness and choose a difficulty from the menu above the grid.
2. Click a cell and enter a digit with the number buttons above and below the grid or with the keyboard; the eraser button clears a cell.
3. Fill every row, column and 3x3 box with the digits 1 to 9, each once.
4. Never repeat a digit along any of the eight diagonal lines.
5. Turn on pencil mode (the pencil button, or Ctrl, Shift or Alt with a number key) to jot candidate digits in a cell.
6. The site tells you when the grid is complete and adds your score; registered players appear on the leaderboards.

Tips

• Treat each diagonal as an extra set of cells a placed digit can see; it removes candidates but never forces a digit to appear.
• Cells where two diagonals cross see the most cells, so they often run out of candidates first.
• Do not hunt for the only place of a digit on a diagonal: unlike X-Sudoku, the digit may not be on that line at all.
• Missed a day? Earlier puzzles are in the archive, and finishing one still counts toward this month's leaderboard.

Questions