Daily logic puzzle
Anti-knight Sudoku online, a new meadow daily.
Anti-knight Sudoku is ordinary Sudoku with one rule added: two cells a chess knight's move apart never hold the same number. Ours is called Hares, it is free, there is no account and no advertising, and a new one appears at midnight.
- a new meadow at midnight, six by six on Monday and Tuesday, nine by nine from Wednesday
- from Friday the non consecutive rule joins in as well
- exactly one solution, reachable by reasoning, checked by program
Today's meadow. The marked leap is the extra rule, two one way and one across.
The rules
Three rules, and that is the whole game.
This variant is also called knight constrained Sudoku. The extra rule is the same under either name.
- Every row, every column and every block holds each number once. A meadow with nine rows has nine columns and nine blocks of three by three; a six by six meadow has blocks of two rows by three columns.
- Hares leap like a knight. Two burrows a knight's leap apart, two one way and one across, never hold the same number. The leap reaches over rows, columns and blocks alike.
- In the harder meadows hares also refuse to sit next to the same number in any direction, corners included. Each puzzle says above it which rules are in force.
Our name for it
We call it Hares.
The variant is known as anti-knight Sudoku. We call ours Hares because a hare leaps the way a knight moves, and because the rule is easier to apply when you picture the animal jumping out of its burrow than when you count squares on a chessboard.
Nothing about ordinary Sudoku changes. What the extra rule adds is reach: a placed number now rules out up to eight more cells scattered across other blocks, which is why anti-knight puzzles can be solved from far fewer givens than a plain grid.
Where to start
Three ways in.
The archive of past meadows is free as well and goes back a year: Hares archive.
- Play today's meadow
The daily puzzle, six by six early in the week and nine by nine from Wednesday, new at midnight.
- How to play anti-knight Sudoku
The rules with a worked example, the controls and what the knight rule rules out.
- Practice sets
Sets by difficulty when one meadow a day is not enough.
One solution
A program says so, not a person.
Every puzzle we publish has exactly one solution, and it is a program that decides. The generator throws a candidate away unless the solver returns exactly one solution and unless a second solver, restricted to human style reasoning, finishes it without guessing.
You can see the check yourself: the file tests.mjs in the game folder runs it over thirty days in every size, with the extra rules switched on exactly as the day requires.
The controls are the ones serious solvers expect: corner marks, centre marks and nine colours, switched with Z, X, C and V, unlimited undo, and a timer that is a score rather than a limit. The shading of a hare's reach is never drawn for you; that is the part you are here to see.
Questions
Questions about anti-knight Sudoku.
What is anti-knight Sudoku?
Ordinary Sudoku with one extra rule: two cells that are a chess knight's move apart, two squares one way and one square across, may not contain the same number. The usual rules still hold, each number once per row, column and block. It is also called knight constrained Sudoku.
Is it free here?
Yes. The daily puzzle, the practice sets, the archive going back a year, the hints and the Check are all free, with no account and no advertising. We sell printable puzzle books on the same site, and that is the whole business model.
Does the knight rule apply across blocks?
Yes. That is what makes the variant interesting: the leap ignores block boundaries entirely, so a number placed in one block rules out cells in three others. In a nine by nine grid a single placement can eliminate up to eight cells that ordinary Sudoku would leave open.
What is the extra rule from Friday on?
The non consecutive rule: two neighbouring cells, corners included, may not hold the same number either. Each puzzle states above the grid which rules are in force, so you are never guessing about the rules themselves.
Do I ever have to guess?
No, and that is checked rather than promised. Every published puzzle was solved by a program restricted to reasoning before it was allowed out. If you are stuck, Hint names the technique and the cell it follows from before it fills anything.
Where can I get more of these on paper?
In the Hares book: one hundred anti-knight Sudoku puzzles as a printable PDF in A4 and US Letter, with the solutions at the back. There is a free five puzzle sample to look at first. See the <a href="/puzzle-books/anti-knight-sudoku-book/">anti-knight Sudoku puzzle book</a>.
Related
More of the same.
One hundred of these on paper, with the solutions at the back: anti-knight Sudoku puzzle book (PDF, free sample).
All ten daily games are on one page: daily logic games.
Auf Deutsch: Anti-knight Sudoku online spielen.