Python/data_structures/binary_tree/binary_tree_traversals.py
Dylan Buchi bf6db32ec2
[mypy] Fix type annotations for binary tree traversals in data structures (#5556)
* [mypy] Fix type annotations for binary tree traversals in data structures

* Change variable name and update level_order_1 to use a deque

Using a deque instead of a list here, because since we are removing from the beginning of the list, the deque will be more efficient.

* remove duplicate function

* Update data_structures/binary_tree/binary_tree_traversals.py

Co-authored-by: John Law <johnlaw.po@gmail.com>

* fix function name at line 137

* Update data_structures/binary_tree/binary_tree_traversals.py

Co-authored-by: John Law <johnlaw.po@gmail.com>

* Update data_structures/binary_tree/binary_tree_traversals.py

Co-authored-by: John Law <johnlaw.po@gmail.com>

* Remove type alias and use the new syntax

* Update data_structures/binary_tree/binary_tree_traversals.py

Co-authored-by: John Law <johnlaw.po@gmail.com>

* Remove prints inside functions and return lists

Co-authored-by: John Law <johnlaw.po@gmail.com>
2021-10-28 22:05:31 +08:00

182 lines
4.7 KiB
Python

# https://en.wikipedia.org/wiki/Tree_traversal
from __future__ import annotations
from collections import deque
from dataclasses import dataclass
from typing import Any, Sequence
@dataclass
class Node:
data: int
left: Node | None = None
right: Node | None = None
def make_tree() -> Node | None:
return Node(1, Node(2, Node(4), Node(5)), Node(3))
def preorder(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) if root else []
def postorder(root: Node | None) -> list[int]:
"""
Post-order traversal visits left subtree, right subtree, root node.
>>> postorder(make_tree())
[4, 5, 2, 3, 1]
"""
return postorder(root.left) + postorder(root.right) + [root.data] if root else []
def inorder(root: Node | None) -> list[int]:
"""
In-order traversal visits left subtree, root node, right subtree.
>>> inorder(make_tree())
[4, 2, 5, 1, 3]
"""
return inorder(root.left) + [root.data] + inorder(root.right) if root else []
def height(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) if root else 0
def level_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] = []
if root is None:
return output
process_queue = deque([root])
while process_queue:
node = process_queue.popleft()
output.append(node.data)
if node.left:
process_queue.append(node.left)
if node.right:
process_queue.append(node.right)
return output
def get_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] = []
def populate_output(root: Node | None, level: int) -> None:
if not root:
return
if level == 1:
output.append(root.data)
elif level > 1:
populate_output(root.left, level - 1)
populate_output(root.right, level - 1)
populate_output(root, level)
return output
def get_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] = []
def populate_output(root: Node | None, level: int) -> None:
if root is None:
return
if level == 1:
output.append(root.data)
elif level > 1:
populate_output(root.right, level - 1)
populate_output(root.left, level - 1)
populate_output(root, level)
return output
def zigzag(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.
"""
if root is None:
return []
output: list[Sequence[Node | None]] = []
flag = 0
height_tree = height(root)
for h in range(1, height_tree + 1):
if not flag:
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
return output
def main() -> 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: ")
for level in range(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__":
import doctest
doctest.testmod()
main()