Frame Sudoku (PuzzleMadness)

About Frame Sudoku (PuzzleMadness)

The usual sudoku rules apply: 1 to 9 once in every row, column and 3x3 box. Outside the grid, every row and column has a clue at both ends, and each clue gives the total of the first three cells from that side. In the site's example the first clue on the left is 14, and the first three cells of that row are 3, 7 and 4.

The site points out one trick that the harder grids need. Each row and column adds up to 45, so if the clues at the two ends of a row are 18 and 16, the three middle cells must total 45 minus 18 minus 16, which is 11. The frame clues also match the box structure, since each clue covers one box's slice of a line, so the three clues for a box's rows (or columns) together add up to 45.

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

1. Open today's Frame 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 first three digits from each edge add up to the clue printed beside them.
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

• Subtract both end clues of a row or column from 45 to get the total of its middle three cells.
• Very small or large clues have few combinations: 6 can only be 1, 2 and 3, and 24 only 7, 8 and 9.
• The three left-hand clues of a box's rows always add up to 45, which is a quick check on your reading of the frame.
• Missed a day? Earlier puzzles are in the archive, and finishing one still counts toward this month's leaderboard.

Questions