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binary_trees.py
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binary_trees.py
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""" Implementations of binary tree algorithms. """
from data_structures import trees
def pre_order(root: trees.BinTreeNode) -> list[int]:
""" Preorder traversal of the binary tree. """
vals = list()
def traverse(root):
if root:
vals.append(root.val)
traverse(root.left)
traverse(root.right)
traverse(root)
return vals
def in_order(root: trees.BinTreeNode) -> list[int]:
""" Inorder traversal of the binary tree. """
vals = list()
def traverse(root):
if root:
traverse(root.left)
vals.append(root.val)
traverse(root.right)
traverse(root)
return vals
def post_order(root: trees.BinTreeNode) -> list[int]:
""" Postorder traversal of the binary tree. """
vals = list()
def traverse(root):
if root:
traverse(root.left)
traverse(root.right)
vals.append(root.val)
traverse(root)
return vals
def from_inorder_postorder(inorder: list[int],
postorder: list[int]) -> trees.BinTreeNode:
""" Builds a binary tree from the lists of inorder, postorder vals. """
inorder_map: dict = {v: i for i, v in enumerate(inorder)}
idx = 1
def build(left: int, right: int):
if left > right:
return
nonlocal idx
root = trees.BinTreeNode(postorder[-idx])
idx += 1
root_id = inorder_map[root.val]
root.right = build(root_id + 1, right)
root.left = build(left, root_id - 1)
return root
return build(0, len(inorder) - 1)
def from_preorder_inorder(inorder: list[int],
preorder: list[int]) -> trees.BinTreeNode:
""" Builds a binary tree from the lists of inorder, preorder vals. """
inorder_map: dict = {v: i for i, v in enumerate(inorder)}
idx = 0
def build(left: int, right: int):
if left > right:
return
nonlocal idx
root = trees.BinTreeNode(preorder[idx])
idx += 1
root_id = inorder_map[root.val]
root.left = build(left, root_id - 1)
root.right = build(root_id + 1, right)
return root
return build(0, len(inorder) - 1)