# List of tickets, in the form (origin, destination)
ORIGINAL_TICKETS = [
('SFO', 'LAX'),
('LAX', 'JFK'),
('JFK', 'LHR'),
('LHR', 'CDG'),
('CDG', 'DXB'),
('DXB', 'HKG'),
('HKG', 'HAM'),
]
Write a function which given the original origin, find the final destination. Then write a function that would find both the original origin and final destination with only access to that ticket list. Finally write a function that finds a missing ticket given the original origin and final destination.