Every section's open seat count and cheapest open seat at each step across a window, in one answer. counts[i] is section sections[i]'s open seats at that step and min_prices[i] is its cheapest open seat at the same instant; null means that section has no reading at or before it, which is NOT the same as zero. Counts carry forward between readings, because an open seat count is a state and not an event, and as_of says how old the newest reading behind a step is. total is the whole house at that step and is null until every section in sections has been read at least once; sections_read says how many of them have, and summing counts yourself gives the part that was read. At most 288 steps, so the step follows the window: omit since and the answer spans the event's own history, fifteen minutes a step across one date and one date a step across a season. An event with no section readings answers an empty frame list, which is the common case. Costs one unit whatever the section count and whatever the window.