Reconstruct Itinerary (with loop/cycle follow-up)

You are given a list of airline tickets tickets, where tickets[i] = [from, to] represents a flight from airport from to airport to. Reconstruct an itinerary that: Uses all tickets exactly once. Starts from "JFK". If multiple valid itineraries exist, returns the lexicographically smallest itinerary when comparing the entire airport sequence. The directed graph may contain loops/cycles and duplicate edges. Output the reconstructed itinerary as a list of airport codes. Input format Line 1: integer n (# of tickets) Next n lines: two strings from to Output format One line: the airport sequence separated by spaces. Typical constraints 1 <= n <= 2*10^5 Example Input: 5 JFK SFO JFK ATL SFO ATL ATL JFK ATL SFO Output: JFK ATL JFK SFO ATL SFO Example Input 5 JFK SFO JFK ATL SFO ATL ATL JFK ATL SFO Output JFK ATL JFK SFO ATL SFO