Anti-Knight Sudoku

How to play anti-knight sudoku

In anti-knight sudoku, two cells a chess knight's move apart (two steps one way, one step the other) can't hold the same digit. Each cell sees up to eight extra cells.

Inside a box the rule adds nothing, because the box already bans repeats. It bites across box borders, where it shapes how each digit can move through a band of three boxes. Our puzzles are set so the knight's moves are needed to finish.

Anti-knight sudoku: full lesson

See the rule in 15 seconds

At a glance

• Cells a knight's move apart can't repeat a digit.
• A cell in the middle of the grid has eight knight's moves.
• The rule only adds anything across box borders.
• Every classic technique still works; the knight only adds eliminations.

The knight's move

The marked cells are a knight's move from the 5. None of them can be 5. The ones in the 5's own box were already ruled out by the box, so the new information is in the boxes around it.

How to start an anti-knight sudoku

1. Scan with the knight

   For each placed digit, cross it off the cells a knight's move away. It's like cross-hatching with an extra pattern.

2. Look at neighboring boxes

   A digit in one box removes up to two cells in each box beside it, on top of the row or column it already rules out. Often that leaves one spot.

3. Check the corners of the grid

   Corner cells have only two knight's moves, but they combine with rows and columns at the edges.

4. Use pairs

   If a digit can only be in two cells of a box, every cell a knight's move from both of them can't be that digit.

5. Mind the givens

   Anti-knight puzzles often start with very few givens. Every one is a source of eliminations.

Common mistakes

Five levels, no guessing

Every puzzle has one solution, proved when it is set, and our solver finishes it by logic alone. The level is the hardest step the solve needs. Here is what each level asks of a anti-knight puzzle:

1. EasySingles, counting knight's moves as extra eliminations.Play Easy
2. MediumPointing pairs and box/line reductions.Play Medium
3. HardNaked and hidden pairs and triples.Play Hard
4. ExpertX-Wings, Skyscrapers and wings.Play Expert
5. FiendishColoring and chains. Never a guess.Play Fiendish

The daily variant rotates through 11 kinds, so a anti-knight daily comes round about every 11 days. Past dailies

Hand-set anti-knight puzzles

Our levels are a good start. For more, Explore has 172 anti-knight puzzles made by people, from Logic Masters and Cracking the Cryptic. A few of the most popular:

One Killer Knightby meggen033Counted Knightsby ScojoAscension (Antiknight Arrows)by Florian WortmannKnights on the Beachby ApricotCoincidenceby JoanieIrish Whispersby JKBongos2 Crosses (Antiknight Sudoku)by Yoshi BaroshiThe knight and the bishopby Ollos

Setters with the most anti-knight puzzles:

• meggen033 31
• Vitray 8
• gwai77 5
• Villse 4
• Daniel Hanson 4
• Florian Wortmann 3
• addie 3
• iEtsh 3
• Aad van de Wetering 3
• billybeth 2

Often combined with:

• Anti-Knight + Killer 70
• Anti-Knight + Kropki 58
• Anti-Knight + Arrow 35
• Anti-Knight + Fog of War 29
• Anti-Knight + Thermo 29
• Anti-Knight + Renban 28
• Anti-Knight + XV 26
• Anti-Knight + German Whispers 25
• Anti-Knight + Anti-King 19
• Anti-Knight + Region Sum Lines 12

All 172 anti-knight puzzles in Explore · Make your own anti-knight sudoku

Questions

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