Find Duplicate Subtrees - Python Leetcode

  Find Duplicate Subtrees

Given the root of a binary tree, return all duplicate subtrees.

For each kind of duplicate subtrees, you only need to return the root node of any one of them.

Two trees are duplicate if they have the same structure with the same node values.

 

Example 1:

Input: root = [1,2,3,4,null,2,4,null,null,4]
Output: [[2,4],[4]]

Example 2:

Input: root = [2,1,1]
Output: [[1]]

Example 3:

Input: root = [2,2,2,3,null,3,null]
Output: [[2,3],[3]]

# Definition for a binary tree node.
# 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]:
        count = collections.Counter()
        trees = collections.defaultdict()
        trees.default_factory = trees.__len__
        ans = []
        def lookup(root):
            if root:
                uid = trees[root.val,lookup(root.left),lookup(root.right)]
                count[uid]+=1
                if count[uid] == 2:
                    ans.append(root)
                return uid
        
        lookup(root)
        return ans
        

TC: O(n) SC: O(n)