def test_rank_zero(bb: bytes) -> None:
assume(len(bb) % 8 == 0)
bits = bitarray()
bits.frombytes(bb)
poppy = Poppy(bits)
for i in range(len(bits)):
assert poppy.rank_zero(i) == sum(1 - int(b) for b in bits[0:(i + 1)])
class Permutation:
def __init__(self, values: IndexedIntSequence) -> None:
runs = self._extract_runs(values)
self._build_huffman_tree(values, runs)
def _extract_runs(self, values: IndexedIntSequence) -> List[HuffmanTreeNode]:
run_starts: List[int] = [0]
for i in range(1, len(values)):
if values[i] < values[i - 1]:
run_starts.append(i)
run_starts_bitarray = bitarray(len(values))
run_starts_bitarray.setall(False)
for start in run_starts:
run_starts_bitarray[start] = True
self._run_starts = Poppy(run_starts_bitarray)
runs: List[HuffmanTreeNode] = []
for i in range(len(run_starts)):
from_index = run_starts[i]
until_index = run_starts[i + 1] if i + 1 < len(run_starts) else len(values)
runs.append(Run(from_=from_index, until=until_index))
return runs
def _build_huffman_tree(self, values: IndexedIntSequence, tree_nodes: List[HuffmanTreeNode]) -> None:
# Determine the tree topology.
heapq.heapify(tree_nodes)
merge_sort_bitarray = bitarray()
merge_sort_offset = 0
while len(tree_nodes) > 1:
x = heapq.heappop(tree_nodes)
y = heapq.heappop(tree_nodes)
merged = HuffmanInnerNode(
size=len(x) + len(y),
left_child=x,
right_child=y,
merge_sort_offset=merge_sort_offset
)
# Populate the merge sort bitarray's values
it_left = ((value, False) for value in x.iterator(values, merge_sort_bitarray))
it_right = ((value, True) for value in y.iterator(values, merge_sort_bitarray))
for _, b in heapq.merge(it_left, it_right):
merge_sort_bitarray.append(b)
merge_sort_offset += 1
heapq.heappush(tree_nodes, merged)
# Build a LOUDS representation of the tree topology
louds = LoudsBinaryTree(
root=tree_nodes[0],
get_left_child=lambda n: n.left_child if isinstance(n, HuffmanInnerNode) else None,
get_right_child=lambda n: n.right_child if isinstance(n, HuffmanInnerNode) else None
)
# The data stored at each node of the tree is:
# - The offset into a bitarray (if a node is an inner node)
# - The offset into the original permutation (if a node is a leaf node)
node_data: List[int] = []
sizes: List[int] = []
queue = deque(tree_nodes)
while queue:
tree_node = queue.popleft()
if isinstance(tree_node, HuffmanInnerNode):
node_data.append(tree_node.merge_sort_offset)
sizes.append(len(tree_node))
queue.append(tree_node.left_child)
queue.append(tree_node.right_child)
elif isinstance(tree_node, Run):
node_data.append(tree_node.from_)
sizes.append(len(tree_node))
else:
raise TypeError
self._louds = louds
self._node_data = node_data
self._merge_sort_poppy = Poppy(merge_sort_bitarray)
number_of_runs = self._run_starts.rank(len(self._run_starts) - 1)
self._run_rank_to_louds_id = [0] * number_of_runs
for louds_id in range(len(self._node_data)):
if self._louds.is_leaf(louds_id):
run_offset = self._node_data[louds_id]
run_rank = self._run_starts.rank(run_offset)
self._run_rank_to_louds_id[run_rank - 1] = louds_id
def __getitem__(self, key: int) -> int:
"""
Retrieve the i'th element of this permutation.
"""
"""
Start at the leaves. Find the index of the current key `k` in the current
node. Now, consider the parent node:
- If the current node is the left child, get the index of the `k`'th
zero in the parent node via "select_zero".
- If the current node is the right child, get the index of the `k`th
one in the parent node via "select".
Repeat until the current node is the root, and return `k`.
"""
run_start = self._run_starts.rank(key) - 1
current_node = self._run_rank_to_louds_id[run_start]
key = key - self._node_data[current_node]
while True:
parent = self._louds.get_parent(current_node)
if parent is None:
return key
else:
parent_offset = self._node_data[parent]
if self._louds.get_left_child(parent) == current_node:
# # get the index of the `k`'th zero in the parent node
parent_rank_zero = (
0 if parent_offset == 0 else
self._merge_sort_poppy.rank_zero(parent_offset - 1)
)
key = self._merge_sort_poppy.select_zero(key + parent_rank_zero) - parent_offset
current_node = parent
else:
# get the index of the `k`th one in the parent node
parent_rank = (
0 if parent_offset == 0 else
self._merge_sort_poppy.rank(parent_offset - 1)
)
key = self._merge_sort_poppy.select(key + parent_rank) - parent_offset
current_node = parent
def index_of(self, value: int) -> int:
"""
Retrieve the index of the given value within this permutation. (This is
the inverse of the permutation.)
"""
"""
Start at the root. Look up the bit at position `value`. Calculate either
the rank_1 or rank_0 of that position, depending on whether it's 1 or 0.
Recurse to either the left or right child, depending on that value.
"""
current_node = self._louds.get_root()
while True:
if self._louds.is_leaf(current_node):
return self._node_data[current_node] + value
else:
offset = self._node_data[current_node]
bit_value = self._merge_sort_poppy[offset + value]
if not bit_value:
value = (
self._merge_sort_poppy.rank_zero(offset + value) -
(
0 if offset == 0 else
self._merge_sort_poppy.rank_zero(offset - 1)
)
) - 1
child = self._louds.get_left_child(current_node)
else:
value = (
self._merge_sort_poppy.rank(offset + value) -
(
0 if offset == 0 else
self._merge_sort_poppy.rank(offset - 1)
)
) - 1
child = self._louds.get_right_child(current_node)
assert child is not None
current_node = child
