def prim(G, start):
pq = PriorityQueue()
for v in G:
v.setDistance(sys.maxsize)
v.setPred(None)
start.setDisatance(0)
pq.build_heap([(v.getDistance(), v) for v in G])
while not pq.is_empty():
currentVert = pq.del_min()
for nextVert in currentVert.getConnections():
newCost = currentVert.getWeight(nextVert)
if nextVert in pq and newCost < nextVert.getDistance():
nextVert.setPred(currentVert)
nextVert.setDisatance(newCost)
pq.decrease_key(nextVert, newCost)
def dijkstra(aGraph, start):
# Actually, it is a priority queue.
pq = PriorityQueue()
start.setDistance(0)
# :meth:`biuld_heap` is O(logV)
pq.build_heap([(v.getDistance(), v) for v in aGraph])
while not pq.is_empty():
# :meth:`del_min()` is O(logV), within the `while` loop, it is O(Vlog(V))
currentVert = pq.del_min()
# The `for` loop is O(E)
for nextVert in currentVert.getConnections():
newDist = currentVert.getDistance() + currentVert.getWeight(
nextVert)
if newDist < nextVert.getDistance():
nextVert.setDistance(newDist)
nextVert.setPred(currentVert)
# :meth:`decrease_key` is within `for` loop, it is O(Elog(V))
pq.decrease_key(nextVert, newDist)
