def generate_tree_postorder(node_lst, root_index):
""" Return the root of the Huffman tree corresponding
to node_lst[root_index].
The function assumes that the list represents a tree in postorder.
@param list[ReadNode] node_lst: a list of ReadNode objects
@param int root_index: index in the node list
@rtype: HuffmanNode
>>> lst = [ReadNode(0, 5, 0, 7), ReadNode(0, 10, 0, 12), \
ReadNode(1, 0, 1, 0)]
>>> generate_tree_postorder(lst, 2)
HuffmanNode(None, HuffmanNode(None, HuffmanNode(5, None, None), \
HuffmanNode(7, None, None)), \
HuffmanNode(None, HuffmanNode(10, None, None), HuffmanNode(12, None, None)))
>>> lst = [ReadNode(0, 70, 0, 93), ReadNode(0, 91, 0, 69), \
ReadNode(0, 76, 0, 73), ReadNode(1, 1, 1, 2), ReadNode(1, 0, 1, 3)]
>>> generate_tree_postorder(lst, 4)
HuffmanNode(None, HuffmanNode(None, HuffmanNode(70, None, None), \
HuffmanNode(93, None, None)), HuffmanNode(None, HuffmanNode(None, \
HuffmanNode(91, None, None), HuffmanNode(69, None, None)), \
HuffmanNode(None, HuffmanNode(76, None, None), HuffmanNode(73, None, None))))
"""
list_node = []
return generate_tree(node_lst, root_index, list_node)
def bytes_to_nodes(buf):
""" Return a list of ReadNodes corresponding to the bytes in buf.
@param bytes buf: a bytes object
@rtype: list[ReadNode]
"""
lst = []
for i in range(0, len(buf), 4):
l_type = buf[i]
l_data = buf[i + 1]
r_type = buf[i + 2]
r_data = buf[i + 3]
lst.append(ReadNode(l_type, l_data, r_type, r_data))
return lst
def bytes_to_nodes(buf):
""" (bytes) -> list of ReadNode
Return a list of ReadNodes corresponding to the bytes in buf.
>>> bytes_to_nodes(bytes([0, 1, 0, 2]))
[ReadNode(0, 1, 0, 2)]
"""
lst = []
for i in range(0, len(buf), 4):
l_type = buf[i]
l_data = buf[i + 1]
r_type = buf[i + 2]
r_data = buf[i + 3]
lst.append(ReadNode(l_type, l_data, r_type, r_data))
return lst
def generate_tree_postorder(node_lst, root_index):
""" Return the root of the Huffman tree corresponding
to node_lst[root_index].
The function assumes that the list represents a tree in postorder.
@param list[ReadNode] node_lst: a list of ReadNode objects
@param int root_index: index in the node list
@rtype: HuffmanNode
>>> lst = [ReadNode(0, 5, 0, 7), ReadNode(0, 10, 0, 12), \
ReadNode(1, 0, 1, 0)]
>>> generate_tree_postorder(lst, 2)
HuffmanNode(None, HuffmanNode(None, HuffmanNode(5, None, None), \
HuffmanNode(7, None, None)), \
HuffmanNode(None, HuffmanNode(10, None, None), HuffmanNode(12, None, None)))
"""
tree = None
nodes = []
index = 0
for item in node_lst:
node = HuffmanNode(None)
# Creates left node
if item.l_type == 0:
node.left = HuffmanNode(item.l_data)
else:
node.left = nodes.pop(0)
# Creates right node
if item.r_type == 0:
node.right = HuffmanNode(item.r_data)
else:
node.right = nodes.pop(0)
nodes.append(node)
if index == root_index:
tree = node
index += 1
return tree
def generate_tree(node_lst_, root_index_, list_node):
""" helper for generate_tree_postorder to reconstruct tree
@param list node_lst_:
@param int root_index_:
@param list list_node:
@rtype: HuffmanNode
>>> lst = [ReadNode(0, 70, 0, 93), ReadNode(0, 91, 0, 69), \
ReadNode(0, 76, 0, 73), ReadNode(1, 1, 1, 2), ReadNode(1, 0, 1, 3)]
>>> list_node = []
>>> generate_tree(lst, 4, list_node)
HuffmanNode(None, HuffmanNode(None, HuffmanNode(70, None, None), \
HuffmanNode(93, None, None)), HuffmanNode(None, HuffmanNode(None, \
HuffmanNode(91, None, None), HuffmanNode(69, None, None)), \
HuffmanNode(None, HuffmanNode(76, None, None), HuffmanNode(73, None, None))))
"""
if len(node_lst_) > 0:
current_node = node_lst_[0]
if current_node.l_type == 0 and current_node.r_type == 0:
new_hfnode = HuffmanNode(None, HuffmanNode(current_node.l_data),
HuffmanNode(current_node.r_data))
list_node.append(new_hfnode)
elif current_node.l_type == 1 and current_node.r_type == 0:
new_hfnode = HuffmanNode(None, list_node[-1],
HuffmanNode(current_node.r_data))
list_node.pop(-1)
list_node.append(new_hfnode)
elif current_node.l_type == 0 and current_node.r_type == 1:
new_hfnode = HuffmanNode(None, HuffmanNode(current_node.l_data),
list_node[-1])
list_node.pop(-1)
list_node.append(new_hfnode)
elif current_node.l_type == 1 and current_node.r_type == 1:
new_hfnode = HuffmanNode(None, list_node[-2], list_node[-1])
list_node.pop(-2)
list_node.pop(-1)
list_node.append(new_hfnode)
node_lst_.pop(0)
generate_tree(node_lst_, root_index_, list_node)
return list_node[0]
"""
