Palindrome Line Sudoku (PuzzleMadness)

About Palindrome Line Sudoku (PuzzleMadness)

Besides the normal sudoku rules (1 to 9 once in each row, column and 3x3 box), the grid carries palindrome lines. Read the digits along a line from one end and then from the other, and you must get the same sequence. In practice this pairs up cells: the first and last cells match, the second and second-to-last match, and so on, while the middle cell of a line with an odd number of cells can be anything.

Equal pairs cannot share a row, column or box, so the lines tend to zig-zag across box borders, and every given digit on a line also tells you its mirror partner. Today's Medium grid, for example, has several long lines, one of them winding down most of the left side of the grid.

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

1. Open today's Palindrome 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 the digits read the same from both ends: the first cell equals the last, the second equals the second-to-last, and so on.
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.

Screenshots

Tips

• Pair up each line's cells from the ends inwards and copy any given digit to its partner straight away.
• Two paired cells hold the same digit, so they rule that digit out of both their rows, columns and boxes.
• Pencil the same candidates into both cells of a pair and update them together.
• Missed a day? Earlier puzzles are in the archive, and finishing one still counts toward this month's leaderboard.

Questions