Reconstruct itinerary with lexicographic ties
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This question evaluates a candidate's ability to model and traverse directed graphs with repeated edges, enforce lexicographic ordering among possible paths, and analyze time and space complexity for an algorithmic solution.
You are given m airline tickets as directed pairs [from, to]. Build an itinerary that starts at a specified airport start (e.g., "JFK") and uses every ticket exactly once. If multiple itineraries are possible, return the lexicographically smallest sequence of airport codes. Tickets may repeat; m can be up to 10^4. Implement the function to return the itinerary, describe your data structures, analyze time and space complexity, and explain how your approach handles cycles and cases where no valid itinerary exists.
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