<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>

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int doBST(TreeNode* root, vector<TreeNode*>& nds, vector<int>& dep) {
        if (root == nullptr) {
            return 0;
        }

        int lc = doBST(root->left, nds, dep);
        int rc = doBST(root->right, nds, dep);

        nds.push_back(root);

        int res = lc > rc ? lc : rc;
        res ++;

        dep.push_back(res);

        return res;
    }

    bool isSame(TreeNode* left, TreeNode* right) {
        if (left == nullptr && right == nullptr) {
            return true;
        }

        if (left == nullptr || right == nullptr) {
            return false;
        }

        if (left->val != right->val) {
            return false;
        }

        return isSame(left->left, right->left) && isSame(left->right, right->right);
    }

    vector<TreeNode*> findDuplicateSubtrees(TreeNode* root) {
        vector<TreeNode*> nds;
        vector<int> deps;
        doBST(root, nds, deps);

        vector<int> cnt(nds.size(), 1);

        for (int i = 1; i < nds.size(); ++ i) {
            for (int j = 0; j < i; ++ j) {
                if (cnt[j] > 0 && deps[i] == deps[j] && isSame(nds[i], nds[j])) {
                    ++ cnt[j];
                    cnt[i] = 0;
                    break;
                }
            }
        }

        vector<TreeNode*> res;
        for (int i = 0; i < nds.size(); ++ i) {
            if (cnt[i] > 1) {
                res.push_back(nds[i]);
            }
        }

        return res;
    }
};
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