花花酱 LeetCode 652. Find Duplicate Subtrees

652. Find Duplicate SubtreesMedium730151FavoriteShare

Given 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 same node values.

Example 1:

The following are two duplicate subtrees:

        1
       / \
      2   3
     /   / \
    4   2   4
       /
      4

2
/
4

and

4

Therefore, you need to return above trees’ root in the form of a list.

Solution 1: Serialization

Time complexity: O(n^2)
Space complexity: O(n^2)

Solution 2: int id for each unique subtree

Time complexity: O(n)
Space complexity: O(n)