LeetCode 652. Find Duplicate Subtrees 递归小坑_def findduplicatesubtrees(self, root: treenode) ->-优快云博客

本文介绍了一种查找二叉树中所有重复子树的方法，并通过示例详细解释了算法的具体实现过程。对于每种类型的重复子树，仅需返回其中一个根节点。

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]]

Constraints:

The number of the nodes in the tree will be in the range [1, 10^4]
-200 <= Node.val <= 200

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# 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]:
        dic,res = {},[]
        
        def dfs(root):
            nonlocal dic,res
            if (root == None):
                return ""
            lstr = dfs(root.left)
            rstr = dfs(root.right)
            total = "{0}-{1}-{2}".format(root.val,lstr,rstr)
            if (total in dic):
                if dic[total] != None: #bug1: add only once
                    res.append(root)
                    dic[total] = None
            else:
                dic[total] = root
            return total
        dfs(root)
        return res