def test_find_cycle_disconnected_graphs(self):
self.graph.add_nodes_from(["A", "B", "C"])
self.graph.add_edges_from_no_data([(10, 11), (12, 10), (11, 12)])
res = retworkx.digraph_find_cycle(self.graph, 0)
self.assertEqual(res, [(0, 1), (1, 2), (2, 3), (3, 0)])
res = retworkx.digraph_find_cycle(self.graph, 10)
self.assertEqual(res, [(10, 11), (11, 12), (12, 10)])
def test_find_cycle_multiple_roots_same_cycles(self):
res = retworkx.digraph_find_cycle(self.graph, 0)
self.assertEqual(res, [(0, 1), (1, 2), (2, 3), (3, 0)])
res = retworkx.digraph_find_cycle(self.graph, 1)
self.assertEqual(res, [(1, 2), (2, 3), (3, 0), (0, 1)])
res = retworkx.digraph_find_cycle(self.graph, 5)
self.assertEqual(res, [])
def test_find_cycle(self):
graph = retworkx.PyDiGraph()
graph.add_nodes_from(list(range(6)))
graph.add_edges_from_no_data([(0, 1), (0, 3), (0, 5), (1, 2), (2, 3),
(3, 4), (4, 5), (4, 0)])
res = retworkx.digraph_find_cycle(graph, 0)
self.assertEqual([(0, 1), (1, 2), (2, 3), (3, 4), (4, 0)], res)
def test_self_loop(self):
self.graph.add_edge(1, 1, None)
res = retworkx.digraph_find_cycle(self.graph, 0)
self.assertEqual([(1, 1)], res)
def test_invalid_types(self):
graph = retworkx.PyGraph()
with self.assertRaises(TypeError):
retworkx.digraph_find_cycle(graph)
def _trial_map(self, digraph: rx.PyDiGraph, sub_digraph: rx.PyDiGraph,
todo_nodes: MutableSet[int],
tokens: MutableMapping[int, int]) -> Iterator[Swap[int]]:
"""Try to map the tokens to their destinations and minimize the number of swaps."""
def swap(node0: int, node1: int) -> None:
"""Swap two nodes, maintaining data structures.
Args:
node0: The first node
node1: The second node
"""
self._swap(node0, node1, tokens, digraph, sub_digraph, todo_nodes)
# Can't just iterate over todo_nodes, since it may change during iteration.
steps = 0
while todo_nodes and steps <= 4 * len(self.graph)**2:
todo_node_id = self.seed.integers(0, len(todo_nodes))
todo_node = tuple(todo_nodes)[todo_node_id]
# Try to find a happy swap chain first by searching for a cycle,
# excluding self-loops.
# Note that if there are only unhappy swaps involving this todo_node,
# then an unhappy swap must be performed at some point.
# So it is not useful to globally search for all happy swap chains first.
cycle = rx.digraph_find_cycle(sub_digraph, source=todo_node)
if len(cycle) > 0:
assert len(cycle) > 1, "The cycle was not happy."
# We iterate over the cycle in reversed order, starting at the last edge.
# The first edge is excluded.
for edge in list(cycle)[-1:0:-1]:
yield edge
swap(edge[0], edge[1])
steps += len(cycle) - 1
else:
# Try to find a node without a token to swap with.
try:
edge = next(edge for edge in rx.digraph_dfs_edges(
sub_digraph, todo_node) if edge[1] not in tokens)
# Swap predecessor and successor, because successor does not have a token
yield edge
swap(edge[0], edge[1])
steps += 1
except StopIteration:
# Unhappy swap case
cycle = rx.digraph_find_cycle(digraph, source=todo_node)
assert len(cycle) == 1, "The cycle was not unhappy."
unhappy_node = cycle[0][0]
# Find a node that wants to swap with this node.
try:
predecessor = next(
predecessor
for predecessor in digraph.predecessor_indices(
unhappy_node) if predecessor != unhappy_node)
except StopIteration:
logger.error(
"Unexpected StopIteration raised when getting predecessors"
"in unhappy swap case.")
return
yield unhappy_node, predecessor
swap(unhappy_node, predecessor)
steps += 1
if todo_nodes:
raise RuntimeError(
"Too many iterations while approximating the Token Swaps.")