def dp_search(digraph, start, end, toPrint = False, visited = None, memo = None):
"""
search of a weighted graph
number of paths is bounded by approximately 3 ** 9000
this will not finish on the full graph
this is for testing on small graphs
visited is a list of strings representing the nodes that have been visited in this path of the recursion tree
visited is used to prevent looping
"""
global num_calls
num_calls += 1
if toPrint:
if num_calls % 100000 == 0:print(num_calls)
# if toPrint:
# print("start: {}; end: {};".format(start.get_streets(), end.get_streets()))
if visited == None:
visited = [str(start)]
# print(type(visited))
else:
visited = visited + [str(start)]
# print(str(start))
if memo == None:
memo = {} #new dict
path = Path(start)
if start == end:
return path
shortest = None
for node in digraph.children_of(start):
if str(node) not in visited: #avoid cycles
try:
new_path = memo[(node, end)]
except(KeyError):
new_path = dp_search(digraph, node, end, toPrint, visited, memo)#find the shortest for this child
if new_path == None: #no valid path was found
continue #try the next child
if shortest == None or new_path < shortest:
memo[(node, end)] = new_path
shortest = new_path
if shortest != None:#a shortest path was found
path.add_path(digraph, shortest)
else:#no children of this node found a valid path
path = None
# pop up
return path
def dynamic_search(digraph, start, end, toPrint = False, visited = None, memo = None):
"""
dynamic programming search of a weighted graph
visited is a list of strings representing the nodes that have been visited in this path of the recursion tree
visited is used to prevent looping
memo is a dictionary of calculated shortest paths; node->path
memo is used to prevent recalculation
"""
if toPrint:
print("start: {}; end: {};".format(start.get_streets(), end.get_streets()))
if memo == None:
memo = {}
if visited == None:
visited = [str(start)]
# print(type(visited))
else:
visited += [str(start)]
# print(str(start))
path = Path(start)
if start == end:
return path
shortest = None
for node in digraph.children_of(start):
if str(node) not in visited: #avoid cycles
try:
new_path = memo[(node, end)] #see if a best shortest path has been calculated from this node
except(KeyError):
new_path = dynamic_search(digraph, node, end, toPrint, visited, memo)#find the shortest for this child
if new_path == None: #no valid path was found
continue #try the next child
if shortest == None or new_path < shortest:
memo[(node, end)] = new_path
shortest = new_path
if shortest != None:#a shortest path was found
path.add_path(digraph, shortest)
else:#no children of this node found a valid path
path = None
# pop up
return path
