Sandwich Sudoku (PuzzleMadness)

About Sandwich Sudoku (PuzzleMadness)

The standard sudoku rules hold: every row, column and 3x3 box contains 1 to 9 once. Each row has a clue on the right and each column a clue along the bottom. Find where the 1 and the 9 sit in that line, add up the digits between them, and the total must equal the clue. In the site's example, the first row has 2, 8, 4, 5, 7 and 3 between its 1 and 9 for a sandwich of 29.

The clues work at both extremes. A sandwich of 0 means the 1 and 9 are next to each other, while a large sandwich of 35 means every other digit sits between them and the 1 and 9 are at the ends of the line. Middle values can be made several ways, so the art is listing the possible fillings and the gap length each needs. The bread is always the same, 1 and 9, which makes those two digits the first to chase in every line.

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. Sandwich Sudoku comes in Easy, Medium, Hard and Tough versions plus a Mixed page, and the same day's Sandwich 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 Sandwich 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 Sandwich Sudoku (PuzzleMadness)

1. Open today's Sandwich 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. Make the digits between the 1 and the 9 in each row and column add up to the clue printed outside that line.
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

• A clue of 0 puts the 1 and the 9 side by side; a clue of 35 puts them at the two ends.
• Small totals need few digits between the bread: a sandwich of 1 is impossible, 2, 3 or 4 means exactly one digit between, and 5 can be one digit or two.
• Place the 1s and 9s across the grid first; once a line's bread is fixed, its clue becomes a simple sum.
• Missed a day? Earlier puzzles are in the archive, and finishing one still counts toward this month's leaderboard.

Questions