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algorithm/data_structures/binary_tree/binary_tree_path_sum.py
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""" | ||
Given the root of a binary tree and an integer target, | ||
find the number of paths where the sum of the values | ||
along the path equals target. | ||
Leetcode reference: https://leetcode.com/problems/path-sum-iii/ | ||
""" | ||
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from __future__ import annotations | ||
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class Node: | ||
""" | ||
A Node has value variable and pointers to Nodes to its left and right. | ||
""" | ||
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def __init__(self, value: int) -> None: | ||
self.value = value | ||
self.left: Node | None = None | ||
self.right: Node | None = None | ||
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class BinaryTreePathSum: | ||
r""" | ||
The below tree looks like this | ||
10 | ||
/ \ | ||
5 -3 | ||
/ \ \ | ||
3 2 11 | ||
/ \ \ | ||
3 -2 1 | ||
>>> tree = Node(10) | ||
>>> tree.left = Node(5) | ||
>>> tree.right = Node(-3) | ||
>>> tree.left.left = Node(3) | ||
>>> tree.left.right = Node(2) | ||
>>> tree.right.right = Node(11) | ||
>>> tree.left.left.left = Node(3) | ||
>>> tree.left.left.right = Node(-2) | ||
>>> tree.left.right.right = Node(1) | ||
>>> BinaryTreePathSum().path_sum(tree, 8) | ||
3 | ||
>>> BinaryTreePathSum().path_sum(tree, 7) | ||
2 | ||
>>> tree.right.right = Node(10) | ||
>>> BinaryTreePathSum().path_sum(tree, 8) | ||
2 | ||
""" | ||
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target: int | ||
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def __init__(self) -> None: | ||
self.paths = 0 | ||
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def depth_first_search(self, node: Node | None, path_sum: int) -> None: | ||
if node is None: | ||
return | ||
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if path_sum == self.target: | ||
self.paths += 1 | ||
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if node.left: | ||
self.depth_first_search(node.left, path_sum + node.left.value) | ||
if node.right: | ||
self.depth_first_search(node.right, path_sum + node.right.value) | ||
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def path_sum(self, node: Node | None, target: int | None = None) -> int: | ||
if node is None: | ||
return 0 | ||
if target is not None: | ||
self.target = target | ||
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self.depth_first_search(node, node.value) | ||
self.path_sum(node.left) | ||
self.path_sum(node.right) | ||
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return self.paths | ||
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if __name__ == "__main__": | ||
import doctest | ||
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doctest.testmod() |