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binary_search_tree.py
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binary_search_tree.py
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""" Binary Search Tree implemented with embedded lists.
Node format: [value, left child, right child].
Leaf nodes look like: [value, [], []].
"""
__author__ = "Caleb Madrigal"
__date__ = "2015-02-25"
def node_value(node, new_value=None):
""" Set value: node_value(node, value); Get value: node_value(node). """
if new_value is not None:
node[0] = new_value
return node[0]
def left_child(node, new_node=None):
""" Set left child: left_child(node, new_left_child); Get left node: left_child(node). """
if new_node is not None:
node[1] = new_node
return node[1]
def right_child(node, new_node=None):
""" Set right child: right_child(node, new_right_child); Get right node: right_child(node). """
if new_node is not None:
node[2] = new_node
return node[2]
def add(tree, value):
""" Adds value to tree and returns tree. """
if tree == []:
tree = [value, [], []]
elif node_value(tree) == None:
node_value(tree, value)
elif value < node_value(tree):
left_child(tree, add(left_child(tree), value))
elif value > node_value(tree):
right_child(tree, add(right_child(tree), value))
# If value == node_value(tree): It's already there - don't reinsert it
return tree
def _find_node(tree, value, parent=None, is_right_child=False):
""" Returns (node, parent, is_right_child_of_parent) if found (parent is None if root).
If not found, return (None, None, False). """
if tree == []:
return (None, parent, is_right_child)
if node_value(tree) == value:
return (tree, parent, is_right_child)
elif value < node_value(tree):
return _find_node(left_child(tree), value, tree, False)
else: # value > node_value(tree)
return _find_node(right_child(tree), value, tree, True)
def contains(tree, value):
""" Returns true if value in tree; False otherwise. """
return _find_node(tree, value)[0] != None
def _find_min_node(tree, parent=None, is_right_child=False):
""" Finds the minimum node in a tree, and returns (node, parent, is_right_child),
where node is the node with the minimum value, parent is the parent of the minimum
node, and is_right_child is true if the minimum node is the right-child of its parent
(or false if it is the left-child of its parent). """
if left_child(tree) == []:
return (tree, parent, is_right_child)
else:
return _find_min_node(left_child(tree), tree, False)
def _remove_node(node_to_remove, parent, is_right_child_of_parent):
# If node not found, return
if not node_to_remove:
return
def set_parent_reference(new_reference):
if parent:
if is_right_child_of_parent:
right_child(parent, new_reference)
else:
left_child(parent, new_reference)
# If the node to be removed has 2 children; Steps:
# * Set the node_to_remove value to the min value in the right subtree
# * call _remove_node() on the item which was swapped with
if left_child(node_to_remove) != [] and right_child(node_to_remove) != []:
(right_child_min_node, rchild_min_node_parent, is_min_right_child) = \
_find_min_node(right_child(node_to_remove), node_to_remove, True)
node_value(node_to_remove, node_value(right_child_min_node))
_remove_node(right_child_min_node, rchild_min_node_parent, is_min_right_child)
# If the node to be removed has just 1 child (the left child), set the parent reference
# to the left child of the node to be removed
elif left_child(node_to_remove) != []:
set_parent_reference(left_child(node_to_remove))
# If the node to be removed has just 1 child (the right child), set the parent reference
# to the right child of the node to be removed
elif right_child(node_to_remove) != []:
set_parent_reference(right_child(node_to_remove))
# The node has no children, so just remove it
else:
set_parent_reference([])
def remove(tree, value):
(node_to_remove, parent, is_right_child_of_parent) = _find_node(tree, value)
_remove_node(node_to_remove, parent, is_right_child_of_parent)
def inorder(tree):
if tree == [] or node_value(tree) == None:
return []
return inorder(left_child(tree)) + [node_value(tree)] + inorder(right_child(tree))
def inorder_traverse(tree, visit_func):
if tree == [] or node_value(tree) == None:
return
inorder_traverse(left_child(tree), visit_func)
visit_func(node_value(tree))
inorder_traverse(right_child(tree), visit_func)
def postorder_traverse(tree, visit_func):
if tree == [] or node_value(tree) == None:
return
postorder_traverse(left_child(tree), visit_func)
postorder_traverse(right_child(tree), visit_func)
visit_func(node_value(tree))
def preorder_traverse(tree, visit_func):
if tree == [] or node_value(tree) == None:
return
visit_func(node_value(tree))
preorder_traverse(left_child(tree), visit_func)
preorder_traverse(right_child(tree), visit_func)
def print_tree(tree, indent=0):
if tree == [] or node_value(tree) == None:
return
print('\t'*indent + str(node_value(tree)))
print_tree(left_child(tree), indent+1)
print_tree(right_child(tree), indent+1)
if __name__ == '__main__':
tree = []
for i in [5, 3, 8, 5, 2, 10, 20, 15, 30, 0, 7]:
tree = add(tree, i)
print("Tree:")
print_tree(tree)
print(tree)
print("Is 5 in tree?", contains(tree, 5))
print("Is 20 in tree?", contains(tree, 20))
print("Is 100 in tree?", contains(tree, 100))
print("Inorder:", inorder(tree))
print("Inorder traversal: ", end="")
inorder_traverse(tree, lambda node: print(node, end=", "))
print("\nPostorder traversal: ", end="")
postorder_traverse(tree, lambda node: print(node, end=", "))
print("\nPreorder traversal: ", end="")
preorder_traverse(tree, lambda node: print(node, end=", "))
print()
remove(tree, 8)
print("Tree after removing 8:")
print_tree(tree)
print("Inorder:", inorder(tree))