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def max_distance(node, ancestors, distances):
"""Calculate the max distance to an ancestor. Return None if"""
best = None
if node in distances:
best = distances[node]
for ancestor in ancestors[node]:
if ancestor not in ancestors:
continue
if ancestor not in distances:
return None
if best is None or distances[ancestor] > best:
best = distances[ancestor] + 1
return best
def farthest_node(graph, ancestors, start):
distances = {start: 0}
lines = set([start])
while len(lines) > 0:
new_lines = set()
for line in lines:
assert line not in graph[line], "%s refers to itself" % line
for descendant in graph[line]:
distance = max_distance(descendant, ancestors, distances)
if distance is None:
continue
distances[descendant] = distance
new_lines.add(descendant)
lines = new_lines
def by_distance(n):
return distances[n]
node_list = distances.keys()
node_list.sort(key=by_distance, reverse=True)
return node_list
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