The Ticket Window Dance

Grand finale: the chaotic ticket window where EVERYTHING happens. 🎟️

You get commands — join:name (back), vip:name (front), serve (front leaves), serve-back (back leaves), rotate:k (front k people cycle to the back, in order). All commands are valid when they arrive. Print the final line front to back, comma-separated, or empty.

Example:

Input: commands = ["join:mia", "join:leo", "vip:kai", "rotate:2", "serve"] Output: kai,mia

Mia and leo join the back, then vip:kai jumps to the front (line: kai, mia, leo). rotate:2 cycles kai and mia to the back (line: leo, kai, mia). Then serve removes leo — leaving kai, mia.