Cinema Seat Allocation

Given n rows of 10 seats and a list of reserved seats, maximize the number of four-person groups that can be placed on adjacent seats within a single row. Because n can be as large as 10^9 but the reserved list is small, treat rows with reservations sparsely (e.g., per-row bitmasks) and determine for each such row which 4-seat blocks remain free; rows without reservations can host two groups.