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652.py
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652.py
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from collections import defaultdict
from typing import List
# Name: Find Duplicate Subtrees
# Link: https://leetcode.com/problems/find-duplicate-subtrees/submissions/
# Method: Solving tidbit
# Time: O(n^2)
# Space: O(n^2)
# Difficulty: Medium
class TreeNode:
def __init__(self, val=0, left=None, right=None):
self.val = val
self.left = left
self.right = right
class Solution:
def findDuplicateSubtrees(self, root: TreeNode) -> List[TreeNode]:
node_repr = defaultdict(list)
def stringify_tree(node: TreeNode):
if not node:
return "null"
left_res = stringify_tree(node.left)
right_res = stringify_tree(node.right)
res = f"{node.val},{left_res},{right_res}"
node_repr[res].append(node)
return res
stringify_tree(root)
return [
tree_roots[0] for tree_roots in node_repr.values() if len(tree_roots) > 1
]