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bus-routes.py 1.05 KB
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Allen Liu 提交于 7年前 . add complexity
# Time: O(|V| + |E|)
# Space: O(|V| + |E|)
import collections
class Solution(object):
def numBusesToDestination(self, routes, S, T):
"""
:type routes: List[List[int]]
:type S: int
:type T: int
:rtype: int
"""
if S == T:
return 0
to_route = collections.defaultdict(set)
for i, route in enumerate(routes):
for stop in route:
to_route[stop].add(i)
result = 1
q = [S]
lookup = set([S])
while q:
next_q = []
for stop in q:
for i in to_route[stop]:
for next_stop in routes[i]:
if next_stop in lookup:
continue
if next_stop == T:
return result
next_q.append(next_stop)
to_route[next_stop].remove(i)
lookup.add(next_stop)
q = next_q
result += 1
return -1
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