Yajilin: arrows and shading
An arrow counts shaded cells in one direction, and shaded cells never touch. Together they pin down where the shading can go.
How it works
An arrow clue counts the shaded cells in its direction, all the way to the edge. Shaded cells never touch side to side, so in a line of cells they need gaps between them.
A 0 is free: every cell it points at is on the loop. When the count is already reached, the rest of the line is on the loop. When the line has just enough room, the shading fits one way.
No touching: once a cell is shaded, every cell beside it that isn’t a clue is on the loop.
Counting room in a line
Count the cells that could still be shaded in the arrow’s direction. Two shaded cells need a gap, so a run of k open cells holds at most (k + 1) ÷ 2 of them, rounded down.
If that maximum equals the clue, the shading alternates and every second cell is settled. Clue cells in the line count for nothing and break it into pieces.
Worth memorizing
A 0 makes its whole line loop cells.
A full arrow: the rest of its line is on the loop.
Shaded cells never touch.
Their neighbors are loop cells.
Practice
0 of 4 rightWhat is the ringed cell?
Using the arrows, what is the ringed cell?
What is the ringed cell?
Using the arrows, what is the ringed cell?