Kirchhoff

Named after Kirchhoff's law of current: what flows into a node must flow back out. This puzzle applies that law to a grid — every cell balances its own books, and that alone is enough to fix one arrangement of arrows.

RULES

• A circled number is a source (+) or a sink (−) with that much to send or absorb.
• A plain number is throughput: how many arrows enter that cell, which is also how many leave.
• Every other cell takes in exactly as much as it gives out.

CONTROLS

• Tap an edge to cycle through the two directions and back to nothing.