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43 lines
873 B
Python
43 lines
873 B
Python
# https://en.wikipedia.org/wiki/Dijkstra's_algorithm in O(E*log(V))
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from heapq import *
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class Edge:
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def __init__(self, t, cost):
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self.t = t
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self.cost = cost
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def dijkstra(graph, s):
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n = len(graph)
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pred = [-1] * n
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prio = [float('inf')] * n
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prio[s] = 0
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q = [(0, s)]
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while q:
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(prio_u, u) = heappop(q)
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if prio_u != prio[u]:
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continue
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for e in graph[u]:
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v = e.t
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nprio = prio[u] + e.cost
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if prio[v] > nprio:
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prio[v] = nprio
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pred[v] = u
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heappush(q, (nprio, v))
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return prio, pred
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def test():
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g = [[] for _ in range(3)]
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g[0].append(Edge(1, 3))
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g[0].append(Edge(2, 2))
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g[1].append(Edge(2, -2))
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dist, pred = dijkstra(g, 0)
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assert dist == [0, 3, 1]
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assert pred == [-1, 0, 1]
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test()
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