Click to cycle empty → ✕ → lock · drag to sweep ✕ · right-click to drop a lock
// one mutex per thread, per resource, per region — adjacency means deadlock
Deadlock is a free daily deduction puzzle for developers. It feels like a queens / region placement challenge with a concurrency metaphor — perfect between meetings.
Place locks so each row, column, and coloured region has exactly one. No two locks may touch — even diagonally. Use Daily for the shared board or Unlimited for more.