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What Is Yajilin?

Yajilin (also known as Yajilin-Kazusan or Arrow Puzzle) is a logic puzzle first published by the Japanese puzzle company Nikoli. The name roughly translates to “arrow link” — a reference to the directional clues and the closed loop you must draw. It sits at the intersection of shading puzzles (like Nurikabe) and path puzzles (like Masyu or Slitherlink), making it a uniquely satisfying challenge.

The puzzle is played on a rectangular grid. Some cells contain an arrow clue: a number paired with a direction (up, down, left, or right). Your task is to shade some empty cells black and then draw a single closed loop (a Hamiltonian cycle) through every remaining white cell. The arrow clues tell you exactly how many shaded cells exist in the direction the arrow points, counting from the clue cell to the edge of the grid.

Rules of Yajilin

1. Arrow clues: Each arrow clue shows a number and a direction. The number indicates how many shaded (black) cells lie in that direction from the clue cell, going to the edge of the grid. Clue cells themselves are neither shaded nor part of the loop.
2. No adjacent shaded cells: Shaded cells may not be orthogonally adjacent (they cannot share an edge). Diagonal adjacency is allowed.
3. Single closed loop: All non-shaded, non-clue cells must be connected by a single closed loop. The loop travels orthogonally (horizontally or vertically) through the centre of each cell.
4. Loop passes through every white cell: Every cell that is not a clue and not shaded must be visited by the loop exactly once.
5. Unique solution: A well-formed Yajilin puzzle has exactly one solution, reachable through pure logic with no guessing.

How to Solve Yajilin Puzzles

1. Start with Zero Clues

An arrow clue showing 0 means there are no shaded cells in that direction. Every cell in that direction (up to the grid edge or the next clue) must be part of the loop. This immediately constrains the loop path and is often the easiest first deduction.

2. Use Maximum-Count Clues

If a clue’s number equals the maximum possible shaded cells in that direction (accounting for the no-adjacency rule), then every valid position in that line must be shaded. For example, an arrow pointing right with the number 2 and only 4 empty cells in that direction means cells must alternate shaded/white.

3. Apply the No-Adjacency Rule

Shaded cells cannot share an edge. Once you place a shaded cell, its four orthogonal neighbours must be either loop cells, clue cells, or the grid edge. This constraint propagates quickly, especially in tight corners.

4. Extend the Loop

If a white cell has only two possible directions for the loop to enter and exit, those segments are forced. Look for cells in corners or near shaded cells that have limited connectivity — the loop path through them is often determined.

5. Avoid Premature Loops

The loop must visit every white cell. If connecting two segments would close the loop before all white cells are included, that connection is impossible. Watch for small isolated regions that would be cut off.

6. Cross-Reference Clues

Multiple clues can constrain the same row or column. If two arrow clues point into the same line from opposite ends, their shaded-cell counts together with the no-adjacency rule can pin down exact placements.

Grid Sizes & Difficulty Levels

• 7×7 — Easy: Compact grid with generous clues. Great for learning the rules and basic techniques.
• 7×7 — Medium/Hard: Same grid size but fewer arrow clues, requiring longer deduction chains and careful loop planning.
• 10×10: The classic Yajilin experience. Balanced density with room for complex shading and loop-path reasoning.
• 14×14: Large grids for experienced solvers. Longer solve times and more intricate interactions between shading and loop constraints.

Yajilin vs Other Logic Puzzles

• vs Nurikabe: Both involve shading cells, but Nurikabe forms a connected sea while Yajilin requires shaded cells to be non-adjacent and adds a loop-drawing element.
• vs Masyu: Both require drawing a single closed loop, but Masyu uses black/white circle clues that constrain turns, while Yajilin uses directional arrow clues that constrain shading.
• vs Slitherlink: Both draw a loop on a grid, but Slitherlink’s clues count edges around a cell, while Yajilin’s clues count shaded cells in a direction.
• vs Hitori: Both shade cells on a grid, but Hitori eliminates duplicate numbers while Yajilin uses arrow clues and requires a Hamiltonian loop through all remaining cells.

Tips for Beginners

• Always process zero-clues first — they are free information.
• Mark cells you know are loop cells; this helps you see forced connections.
• If stuck, look for dead ends — cells with only one possible path in or out.
• Remember: every white cell must be on the loop. If a cell can’t connect, it’s shaded.
• Start on 7×7 Easy to build confidence before moving to larger grids.

Frequently Asked Questions

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