Entropic Line Sudoku (PuzzleMadness)

About Entropic Line Sudoku (PuzzleMadness)

Every row, column and 3x3 box holds 1 to 9 once, as in any sudoku. Along each Entropic line, pick any three neighbouring cells and you must find exactly one low digit (1, 2 or 3), one medium (4, 5 or 6) and one high (7, 8 or 9). In the site's example, one line reads 6, 7, 2, 6, 9, 2, 4, 7, 3: medium, high, low, repeating.

That means the groups repeat in a fixed cycle along a line: cells three steps apart always belong to the same group. Find the group of any three neighbouring cells on a line and you know the group of every cell on it. It is the line-shaped cousin of Entropy Sudoku, where the low, medium and high rule applies to 2x2 blocks instead.

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

1. Open today's Entropic Line 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. Along each grey line, make every run of three neighbouring cells contain one low (1 to 3), one medium (4 to 6) and one high (7 to 9) digit.
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

• Cells three steps apart on a line share a group, so label the line in a repeating pattern of three once you know any part of it.
• Pencil L, M or H first and choose exact digits later.
• A long line inside a single box uses up all three groups quickly, which limits what the rest of the box can hold.
• Missed a day? Earlier puzzles are in the archive, and finishing one still counts toward this month's leaderboard.

Questions