<p>Given the <code>root</code>&nbsp;of a binary tree, return all <strong>duplicate subtrees</strong>.</p>

<p>For each kind of duplicate subtrees, you only need to return the root node of any <b>one</b> of them.</p>

<p>Two trees are <strong>duplicate</strong> if they have the <strong>same structure</strong> with the <strong>same node values</strong>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/08/16/e1.jpg" style="width: 450px; height: 354px;" />
<pre>
<strong>Input:</strong> root = [1,2,3,4,null,2,4,null,null,4]
<strong>Output:</strong> [[2,4],[4]]
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/08/16/e2.jpg" style="width: 321px; height: 201px;" />
<pre>
<strong>Input:</strong> root = [2,1,1]
<strong>Output:</strong> [[1]]
</pre>

<p><strong class="example">Example 3:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2020/08/16/e33.jpg" style="width: 450px; height: 303px;" />
<pre>
<strong>Input:</strong> root = [2,2,2,3,null,3,null]
<strong>Output:</strong> [[2,3],[3]]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of the nodes in the tree will be in the range <code>[1, 5000]</code></li>
	<li><code>-200 &lt;= Node.val &lt;= 200</code></li>
</ul>

class Solution {
public:
string dfs(TreeNode* root,vector<TreeNode*>& res,map<string,TreeNode*>& hash,map<string,int>& ct){
    if(root==NULL){
        return "n";
    }
    string tmp="";
    tmp+=to_string(root->val)+","+dfs(root->left,res,hash,ct)+","+dfs(root->right,res,hash,ct);
    // if(hash.find(tmp)!=hash.end())res.push_back(hash[tmp]);
    if(ct.find(tmp)!=ct.end() && ct[tmp]==1){
        res.push_back(hash[tmp]);
    }
    hash[tmp]=root;
    ct[tmp]++;
    return tmp;
}

    vector<TreeNode*> findDuplicateSubtrees(TreeNode* root) {
        vector<TreeNode*>res;
        map<string,TreeNode*>hash;
        map<string,int>ct;
        string dummy=dfs(root,res,hash,ct);
        return res;
    }
};
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