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# Generate all possible single-root message thread structures of size
# argv[1]. Each output line is a thread structure, where the n'th
# field is either a number giving the parent of message n or "None"
# for the root.
import sys
from itertools import chain, combinations
def subsets(s):
return chain.from_iterable(combinations(s, r) for r in range(len(s)+1))
nodes = set(range(int(sys.argv[1])))
# Queue of (tree, free, to_expand) where tree is a {node: parent}
# dictionary, free is a set of unattached nodes, and to_expand is
# itself a queue of nodes in the tree that need to be expanded.
# The queue starts with all single-node trees.
queue = [({root: None}, nodes - {root}, (root,)) for root in nodes]
# Process queue
while queue:
tree, free, to_expand = queue.pop()
if len(to_expand) == 0:
# Only print full-sized trees
if len(free) == 0:
print(" ".join(map(str, [msg[1] for msg in sorted(tree.items())])))
else:
# Expand node to_expand[0] with each possible set of children
for children in subsets(free):
ntree = {child: to_expand[0] for child in children}
ntree.update(tree)
nfree = free.difference(children)
queue.append((ntree, nfree, to_expand[1:] + tuple(children)))
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