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Program to find airports in correct order in Python?
Suppose we have a list of flights as [origin, destination] pairs. The list is shuffled; we have to find all the airports that were visited in the correct order. If there are more than one valid itinerary, return lexicographically smallest ones first.
So, if the input is like flights = [["Mumbai", "Kolkata"],["Delhi", "Mumbai"],["Kolkata", "Delhi"] ], then the output will be ['Delhi', 'Mumbai', 'Kolkata', 'Delhi']
To solve this, we will follow these steps
ins := an empty map
outs := an empty map
adj_list := an empty map
Define a function dfs() . This will take airport
while outs[airport] is not null, do
nxt := size of adj_list[airport] - outs[airport]
outs[airport] := outs[airport] - 1
insert airport at the end of ans
Define a method called solve(), this will take flights
for each start end pair s, e in flights, do
insert e at the end of adj_list[s]
outs[s] := outs[s] + 1
ins[e] := ins[e] + 1
for each l in list of all values of adj_list, do
sort the list l
start := null, end := null
for each airport in list of all keys of adj_list, do
if outs[airport] - ins[airport] is same as 1, then
if start not null, then
return
start := airport
otherwise when outs[airport] - ins[airport] is same as -1, then
if end is not null, then
return
end := airport
otherwise when outs[airport] - ins[airport] is not same as 0, then
return
start := start if start is not null otherwise minimum of all keys of adj_list
ans := a new list
dfs(start)
return reverse of ans
From the main method call solve(flights)
Example
from collections import defaultdict class Solution: def solve(self, flights): ins = defaultdict(int) outs = defaultdict(int) adj_list = defaultdict(list) for s, e in flights: adj_list[s].append(e) outs[s] += 1 ins[e] += 1 for l in adj_list.values(): l.sort() start = None end = None for airport in adj_list.keys(): if outs[airport] - ins[airport] == 1: if start: return start = airport elif outs[airport] - ins[airport] == -1: if end: return end = airport elif outs[airport] - ins[airport] != 0: return start = start if start else min(adj_list.keys()) ans = [] def dfs(airport): while outs[airport]: nxt = len(adj_list[airport]) - outs[airport] outs[airport] -= 1 dfs(adj_list[airport][nxt]) ans.append(airport) dfs(start) return ans[::-1] ob = Solution() flights = [ ["Mumbai", "Kolkata"], ["Delhi", "Mumbai"], ["Kolkata", "Delhi"] ] print(ob.solve(flights))
Input
[["Mumbai", "Kolkata"], ["Delhi", "Mumbai"], ["Kolkata", "Delhi"] ]
Output
['Delhi', 'Mumbai', 'Kolkata', 'Delhi']
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