Python/data_structures/binary_tree/binary_tree_traversals.py at master · imanghotbi-python/Python · GitHub

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# https://en.wikipedia.org/wiki/Tree_traversal
from __future__ importannotations

fromcollectionsimportdeque
fromcollections.abcimportSequence
fromdataclassesimportdataclass
fromtypingimportAny


@dataclass
classNode:
data: int
left: Node|None=None
right: Node|None=None


defmake_tree() ->Node|None:
r"""
 The below tree
 1
 / \
 2 3
 / \
 4 5
 """
tree=Node(1)
tree.left=Node(2)
tree.right=Node(3)
tree.left.left=Node(4)
tree.left.right=Node(5)
returntree


defpreorder(root: Node|None) ->list[int]:
"""
 Pre-order traversal visits root node, left subtree, right subtree.
 >>> preorder(make_tree())
 [1, 2, 4, 5, 3]
 """
return [root.data] +preorder(root.left) +preorder(root.right) ifrootelse []


defpostorder(root: Node|None) ->list[int]:
"""
 Post-order traversal visits left subtree, right subtree, root node.
 >>> postorder(make_tree())
 [4, 5, 2, 3, 1]
 """
returnpostorder(root.left) +postorder(root.right) + [root.data] ifrootelse []


definorder(root: Node|None) ->list[int]:
"""
 In-order traversal visits left subtree, root node, right subtree.
 >>> inorder(make_tree())
 [4, 2, 5, 1, 3]
 """
returninorder(root.left) + [root.data] +inorder(root.right) ifrootelse []


defheight(root: Node|None) ->int:
"""
 Recursive function for calculating the height of the binary tree.
 >>> height(None)
 0
 >>> height(make_tree())
 3
 """
return (max(height(root.left), height(root.right)) +1) ifrootelse0


deflevel_order(root: Node|None) ->Sequence[Node|None]:
"""
 Returns a list of nodes value from a whole binary tree in Level Order Traverse.
 Level Order traverse: Visit nodes of the tree level-by-level.
 """
output: list[Any] = []

ifrootisNone:
returnoutput

process_queue=deque([root])

whileprocess_queue:
node=process_queue.popleft()
output.append(node.data)

ifnode.left:
process_queue.append(node.left)
ifnode.right:
process_queue.append(node.right)
returnoutput


defget_nodes_from_left_to_right(
root: Node|None, level: int
) ->Sequence[Node|None]:
"""
 Returns a list of nodes value from a particular level:
 Left to right direction of the binary tree.
 """
output: list[Any] = []

defpopulate_output(root: Node|None, level: int) ->None:
ifnotroot:
return
iflevel==1:

output.append(root.data)
eliflevel>1:
populate_output(root.left, level-1)
populate_output(root.right, level-1)

populate_output(root, level)
returnoutput


defget_nodes_from_right_to_left(
root: Node|None, level: int
) ->Sequence[Node|None]:
"""
 Returns a list of nodes value from a particular level:
 Right to left direction of the binary tree.
 """
output: list[Any] = []

defpopulate_output(root: Node|None, level: int) ->None:
ifrootisNone:
return
iflevel==1:
output.append(root.data)
eliflevel>1:
populate_output(root.right, level-1)
populate_output(root.left, level-1)

populate_output(root, level)
returnoutput


defzigzag(root: Node|None) ->Sequence[Node|None] |list[Any]:
"""
 ZigZag traverse:
 Returns a list of nodes value from left to right and right to left, alternatively.
 """
ifrootisNone:
return []

output: list[Sequence[Node|None]] = []

flag=0
height_tree=height(root)

forhinrange(1, height_tree+1):
ifnotflag:
output.append(get_nodes_from_left_to_right(root, h))
flag=1
else:
output.append(get_nodes_from_right_to_left(root, h))
flag=0

returnoutput


defmain() ->None: # Main function for testing.
"""
 Create binary tree.
 """
root=make_tree()
"""
 All Traversals of the binary are as follows:
 """

print(f"In-order Traversal: {inorder(root)}")
print(f"Pre-order Traversal: {preorder(root)}")
print(f"Post-order Traversal: {postorder(root)}", "\n")

print(f"Height of Tree: {height(root)}", "\n")

print("Complete Level Order Traversal: ")
print(level_order(root), "\n")

print("Level-wise order Traversal: ")

forlevelinrange(1, height(root) +1):
print(f"Level {level}:", get_nodes_from_left_to_right(root, level=level))

print("\nZigZag order Traversal: ")
print(zigzag(root))


if__name__=="__main__":
importdoctest

doctest.testmod()
main()