Yajilin

The Yajilin (also called Arrow Ring) puzzle is played on a grid of squares. At the beginning, cells are either labeled (containing a number and an arrow) or empty. Black cells, an additional cell type, may be discovered during the solving process.

The goal is to draw a single continuous non-intersecting loop that passes through each cell that is neither black nor labeled. The loop must enter each cell from an edge, turn 90 degrees and then exit through an edge.

For each labeled cell, its number indicates the count of the black cells that lie in that row or column in the direction of its arrow. Labeled cells can never be black, and do not count as a black cell for the purpose of satisfying other labeled cells, also the loop cannot pass through them.

Black cells never share a side and there may be black cells that are not accounted for by the labeled cells.