def CalculateSSSPDEQI(srcNodeID, numNode, dist, pred):
""" Deque implementation of MLC using list and Dr. Zhou's approach.
The time complexities of pop(0) and insert(0, x) for built-in list are both
O(n), where n is the size of list at run time.
"""
status = [0 for i in range(numNode)]
dist[srcNodeID] = 0
# list
selist = []
selist.append(srcNodeID)
status[srcNodeID] = 1
# label correcting
while selist:
i = selist.pop(0)
# 2 indicates the current node p appeared in selist before
# but is no longer in it.
status[i] = 2
pNode = GetNode(i)
for linkIDX in pNode.GetOutgoingLinks():
pLink = GetLink(linkIDX)
j = pLink.GetDestNodeID()
if dist[j] > dist[i] + pLink.GetLen():
dist[j] = dist[i] + pLink.GetLen()
pred[j] = i
if status[j] != 1:
if status[j] == 2:
selist.insert(0, j)
else:
selist.append(j)
status[j] = 1
def CalculateSSSPFIFOII(srcNodeID, numNode, dist, pred):
""" FIFO implementation of MLC using built-in list and indicator array
x in s operation for built-in list can be replaced using an
indicator/status array. The time complexity is only O(1).
"""
status = [0 for i in range(numNode)]
dist[srcNodeID] = 0
# list
selist = []
selist.append(srcNodeID)
status[srcNodeID] = 1
# label correcting
while selist:
i = selist.pop(0)
status[i] = 0
pNode = GetNode(i)
for linkIDX in pNode.GetOutgoingLinks():
pLink = GetLink(linkIDX)
j = pLink.GetDestNodeID()
if dist[j] > dist[i] + pLink.GetLen():
dist[j] = dist[i] + pLink.GetLen()
pred[j] = i
if not status[j]:
selist.append(j)
status[j] = 1
def CalculateSSSPDijkstraII(srcNodeID, dist, pred):
""" Minimum Distance Label Implementation using heap
heappop(h) from heapq involves two operations:
1. Find the object with the minimum key from heap h;
2. Delete the object with the minimum key from heap h.
As h is a binary heap, the two operations require O(1) time and O(logn)
time respectively. The overall time complexity of these two operations is
O(logn) compared to O(n) in the implementation without heap.
NOTE that this implementation is DIFFERENT with the standard heap
implementation of Dijkstra's Algorithm as there is no
decrease-key(h, newval, i) in heaqp from Python STL to reduce the key of an
object i from its current value to newval.
Omitting decrease-key(h, newval, i) WOULD NOT affect the correctness of the
implementation.
"""
dist[srcNodeID] = 0
# heap
selist = []
heapq.heapify(selist)
heapq.heappush(selist, (dist[srcNodeID], srcNodeID))
# label correcting
while selist:
(k, i) = heapq.heappop(selist)
pNode = GetNode(i)
for linkIDX in pNode.GetOutgoingLinks():
pLink = GetLink(linkIDX)
j = pLink.GetDestNodeID()
if dist[j] > k + pLink.GetLen():
dist[j] = k + pLink.GetLen()
pred[j] = i
heapq.heappush(selist, (dist[j], j))
def CalculateSSSPDijkstraI(srcNodeID, numNode, dist, pred):
""" Minimum Distance Label Implementation without heap
There are two major operations with this implementation:
1. Find the node with the minimum distance label from the scan eligible
list by looping through all the nodes in this list, which takes O(n)
time;
2. Remove this node from list by the built-in remove() operation, which
takes O(n) time as well.
The overall time complexity of these two operations is O(n), where, n is
the list size at run time.
"""
status = [0 for i in range(numNode)]
dist[srcNodeID] = 0
# list
selist = []
selist.append(srcNodeID)
status[srcNodeID] = 1
# label correcting
while selist:
i = GetNextNodeID(selist, dist)
selist.remove(i)
status[i] = 0
pNode = GetNode(i)
for linkIDX in pNode.GetOutgoingLinks():
pLink = GetLink(linkIDX)
j = pLink.GetDestNodeID()
if dist[j] > dist[i] + pLink.GetLen():
dist[j] = dist[i] + pLink.GetLen()
pred[j] = i
if not status[j]:
selist.append(j)
status[j] = 1
def CalculateSSSPFIFOI(srcNodeID, dist, pred):
""" FIFO implementation of MLC using built-in list and x in s operation
The time complexity of x in s operation for built-in list is O(n), where n
is the size of list at run time.
"""
dist[srcNodeID] = 0
# list
selist = []
selist.append(srcNodeID)
# label correcting
while selist:
i = selist.pop(0)
pNode = GetNode(i)
for linkIDX in pNode.GetOutgoingLinks():
pLink = GetLink(linkIDX)
j = pLink.GetDestNodeID()
if dist[j] > dist[i] + pLink.GetLen():
dist[j] = dist[i] + pLink.GetLen()
pred[j] = i
if j not in selist:
selist.append(j)
def CalculateSSSPDEQII(srcNodeID, numNode, dist, pred):
""" Deque implementation of MLC using deque and Dr. Zhou's approach.
The computation efficiency can be improve by replacing built-in list with
deque as well as the following operations:
1. popleft(),
2. appendleft(x).
Their running times are both O(1).
See https://github.com/jdlph/Path4GMNS for more effecient implementation
"""
status = [0 for i in range(numNode)]
dist[srcNodeID] = 0
# deque, choose one of the following three
selist = collections.deque()
# selist = SimpleDequePy(numNode)
# selist = SimpleDequeC.deque(numNode)
selist.append(srcNodeID)
status[srcNodeID] = 1
# label correcting
while selist:
i = selist.popleft()
# 2 indicates the current node p appeared in selist before
# but is no longer in it.
status[i] = 2
pNode = GetNode(i)
for linkIDX in pNode.GetOutgoingLinks():
pLink = GetLink(linkIDX)
j = pLink.GetDestNodeID()
if dist[j] > dist[i] + pLink.GetLen():
dist[j] = dist[i] + pLink.GetLen()
pred[j] = i
if status[j] != 1:
if status[j] == 2:
selist.appendleft(j)
else:
selist.append(j)
status[j] = 1