Python Challenges: Compute the person's itinerary from a given unordered list of flights

Python Challenges - 1: Exercise-55 with Solution

Given an unordered list of flights taken by someone, each represented as (origin, destination) pairs, and a starting airport.
Write a Python program to compute the person's itinerary. If no such itinerary exists, return null. If there are multiple possible itineraries, return the lexicographically smallest one. All flights must be used in the itinerary.
For example, given the list of flights [('SFO', 'HKO'), ('YYZ', 'SFO'),
('YUL', 'YYZ'), ('HKO', 'ORD')] and starting airport 'YUL', you should return the list ['YUL', 'YYZ', 'SFO', 'HKO', 'ORD'].
Given the list of flights [('SFO', 'COM'), ('COM', 'YYZ')] and starting airport 'COM', you should return null.
Given the list of flights [('A', 'B'), ('A', 'C'), ('B', 'C'), ('C', 'A')]
and starting airport 'A', you should return the list ['A', 'B', 'C', 'A', 'C']
even though ['A', 'C', 'A', 'B', 'C'] is also a valid itinerary. However, the first one is lexicographically smaller.

Sample Solution:

Python Code:

def intinerary(llist, start):
    #Ref.https://bit.ly/2Pb67Bk    
    itinerary_list = []
    itinerary_list.append(start)

    while len(llist) >= 1:
        current = None
        directions = {}

        for item in llist:
           
            if item[0] == start:
                directions[item[0]] = item[1]

        if len(directions) >= 1:
            current = min(directions.values())
            remove_tuple = (start, current)

        try:
            llist.remove(remove_tuple)
            itinerary_list.append(current)
            start = current
        except:
            return "not valid intinerary"

    return itinerary_list


print(intinerary([('SFO', 'HKO'), ('YYZ', 'SFO'), ('YUL', 'YYZ'), ('HKO', 'ORD')], 
    'YUL'))

print(intinerary([('SFO', 'COM'), ('COM', 'YYZ')], 
    'COM'))

print(intinerary([('A', 'B'), ('A', 'C'), ('B', 'C'), ('C', 'A')], 
    'A'))

Sample Output:

['YUL', 'YYZ', 'SFO', 'HKO', 'ORD']
not valid intinerary
['A', 'C', 'A', 'B', 'C']

Flowchart:

Python Code Editor:

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