def singleSourceShortestPath(graph, s):
"""Compute and return (dist, pred) matrices of computation"""
pq = BHeap(len(graph))
dist = {}
pred = {}
for v in graph:
dist[v] = sys.maxint
pred[v] = None
dist[s] = 0
for v in graph:
pq.insert(v, dist[v])
while not pq.isEmpty():
u = pq.smallest()
for v in graph[u]:
wt = graph[u][v]
newLen = dist[u] + wt
if newLen < dist[v]:
pq.decreaseKey(v, newLen)
dist[v] = newLen
pred[v] = u
return (dist, pred)
def computeMST(graph):
"""Return set of edges that forms MST starting search from s"""
key = {}
pred = {}
inqueue = {}
for v in graph:
key[v] = sys.maxint
pred[v] = None
# choose any vertex to start from. Use last from previous loop
key[v] = 0
pq = BHeap(len(graph))
for v in graph:
pq.insert(v, key[v])
inqueue[v] = True
while not pq.isEmpty():
u = pq.smallest()
inqueue[u] = False
for v in graph[u]:
if inqueue[v]:
wt = graph[u][v]
if wt < key[v]:
pred[v] = u
key[v] = wt
pq.decreaseKey(v, wt)
return pred
