Problem URL: Destination city

The destination city can not be seen as departure city. So, we will create a set with all departure cities. Then we iterate all destination cities and check if it is in the set. If not, we return it.

class Solution:
    def destCity(self, paths: List[List[str]]) -> str:
        departures = set()
        for src, dest in paths:
            departures.add(src)
        for src, dest in paths:
            if dest not in departures:
                return dest

Time Complexity: O(n)
Space Complexity: O(n)