Implement a seat booking system for an Upstox event. Seats are numbered from 1 to capacity, and each user may hold at most one seat at a time.
Process operations in order. For a reserve operation, assign the smallest available seat to the user. Return the assigned seat number, or -1 if the user already has a seat or no seats remain. For a cancel operation, release the user's seat and return its number, or return -1 if the user has no active reservation.
Use a set to track available seats and appropriate set or map structures to prevent duplicate active reservations.
Implement seat_booking(capacity, operations).
capacity is an integer.operations is a list of two-item lists: [action, user].action is either "reserve" or "cancel".user is a non-empty string.reserve or canceldef seat_booking(capacity, operations):