I'm having trouble finding a way to build a tree path from a list of related tuples? I only want a list of every path where each node is visited once, aka hamiltonian path.
I keep getting close but missing some path.
For example, let's say we have this list of connections:
connections = [(1, 4), (1, 5), (2, 5), (3, 4), (4, 1), (4, 3), (4, 5), (5, 1), (5, 2), (5, 4)]
desired output:
[[1,4,3], [1,4,5,2], [1,5,2], [1,5,4,3],
[2,5,1,4,3], [2,5,4,1], [2,5,4,3],
[3,4,1,5,2], [3,4,5,1], [3,4,5,2],
[4, 3], [4,1,5,2], [4,5,1], [4,5,2],
[5, 2], [5,1,4,3], [5,4,1], [5,4,3]
]
So each possible path is stored and each node is visited only once:
Here's what I have but it's missing a lot of paths:
def find_paths(current_vertex):
if current_vertex not in current_path:
current_path.append(current_vertex)
possible_next_verticies = [v2 for v1,v2 in connections if v1 == current_vertex]
# if the current vertex is in the current_path
if current_vertex in current_path:
# if all the possible_next_vertices are in the current_path, return
adjacencies = [v for v in possible_next_verticies if v not in current_path]
if not adjacencies:
print "current_path: %s" % current_path
if current_path not in TESTED_PATHS:
TESTED_PATHS.append(current_path)
current_path.remove(current_vertex)
return
for next_vertice in possible_next_verticies:
if next_vertice not in current_path:
current_path.append(next_vertice)
find_paths(next_vertice)
continue
else:
continue
return current_path
OK, I was having so much trouble because of the data structure I was trying to work from, since there were duplicates in the original connections graph.
Better is to use a data structure like this:
connections = {1: [4, 5], 2: [5], 3: [4], 4: [1, 3, 5], 5: [1, 2, 4]}
Then the following two algorithms can be used from https://www.python.org/doc/essays/graphs/
def find_path(graph, start, end, path=[]):
path = path + [start]
if start == end:
return path
if not graph.has_key(start):
return None
for node in graph[start]:
if node not in path:
newpath = find_path(graph, node, end, path)
if newpath: return newpath
return None
and for the full paths
def find_all_paths(graph, start, end, path=[]):
path = path + [start]
if start == end:
return [path]
if not graph.has_key(start):
return []
paths = []
for node in graph[start]:
if node not in path:
newpaths = find_all_paths(graph, node, end, path)
for newpath in newpaths:
paths.append(newpath)
return paths