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#!/usr/bin/env python3
import sys
def no_connection(routes: list) -> str:
# Calculate a list of origins (first value) and destinations (second value)
origins = [v[0] for v in routes]
destinations = [v[1] for v in routes]
# Find route destinations that aren't also an origin
dead_ends = [d for d in destinations if d not in origins]
if len(dead_ends) > 1:
raise ValueError(
'There are multiple routes with no outgoing connection')
if len(dead_ends) == 0:
raise ValueError('All routes have an outgoing connection')
return dead_ends[0]
def main():
# Convert input into pairs. The first value is the start of route.
# The second value is the destination
routes = []
for i in range(1, len(sys.argv), 2):
routes.append([sys.argv[i], sys.argv[i+1]])
result = no_connection(routes)
print(result)
if __name__ == '__main__':
main()
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