652.py

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
 ]